First attempt to remove commodity set and replace it with a parameter telling if ts_priceChange should be used

Issue #161

- q_transferTwoWayLimit1 is used if investments not enabled
- q_transferTwoWayLimit2 is used if investments enabled and initial capacities are the same in both directions

If investments are enabled and initial capacities are not the same in both directions, a similar constraint would become nonlinear.

Issue #158

From user perspective:
- Deleting the p_groupPolicy(group, 'energyMaxVgenSign') parameter. For a minimum energy constraint, the user should now add a positive p_groupPolicy(group, 'energyMin').
- For constraints with p_groupPolicy(group, 'energyShareMax') or p_groupPolicy(group, 'energyShareMin'), the user should now also add the consumption units to be considered in the constraint to gnuGroup. Previously they were automatically considered if they connected to nodes in gnGroup. This was problematic for storage units.

From model code perspective:
- Rearranging q_energyMax(group), q_energyShareMax(group), and q_energyShareMin(group) constraints to q_energyLimit(group, min_max) and q_energyShareLimit(group, min_max) constraints.

Issue #157

Issue #137

1) Updating 1e_scenChanges.gms according to the new inputs, 2) adding a new constraint q_unitGreaterThanConstraint, and 3) fixing a few constraints to work with the invest model as well.

First working commit for the new inputs and outputs system. Probably buggy... In Google Drive there is 8unit system excel that works with this (vInputOutput.xlsx).

Removing q_resDemandLargestInfeedTransferUp and q_resDemandLargestInfeedTransferDown, as q_resDemandLargestInfeedTransfer can handle both.

Adding a new constraint q_maxDownward2 and modifying q_rampDownLimit. A small change to v_reserve.up to make it work with consumption units as well.

q_maxDownward2: similar to q_maxUpward2 but for v_gen and downward online+offline reserve provision

q_rampDownLimit: do not consider offline reserve provision

q_maxUpward: Moving "not nuOfflineRescapable(restype, node, unit)" from equation condition to a condition for summing reserve variables

q_maxUpward2: Removing many of the equation conditions (does not apply to consumption units, for example), cleaning up terms in the equation (hopefully not removing anything that should have stayed)

q_maxUpward3: Not sure if this constraint is needed, so ignoring it in invest and schedule models -- can be included again if needed

q_reserveProvision2: Some refinements to the equation conditions and the equation terms in order to make the constraint limit the online reserve provision of units with online variables

q_rampUpLimit: Moving "not nuOfflineRescapable(restype, node, unit)" from equation condition to a condition for summing reserve variables

q_rampUpLimit2: Not sure if this constraint is needed, so ignoring it in invest and schedule models -- can be included again if needed.

Making it possible to choose in the modelsInit.gms file whether to include the two additional incremental heat rate equations that use binary variables:
- mSettings(m, 'incHRAdditionalConstraints') = 0: use the constraints but only for units with non-convex fuel use
- mSettings(m, 'incHRAdditionalConstraints') = 1: use the constraints for all units represented using incremental heat rates
Enabling incremental heat rates also in the invest model (and potentially in the building model). Some clean-up to the incremental heat rate equations.

Implementing cyclic online states for units (inside/between samples). A new set uss(unit, s, s) added for this purpose. See issue #51.

-Removing the unitFail set (unit_fail set is directly read from the input GDX)
-Deleting N-1 param_policy (Infeed2Cover can handle its task)

Use --input_dir=<path> and --output_dir=<path>. Defaults are ./input and ./output, respectively.

Additional constraints need to be declared too when a model is initialized. Added reading of corresponding input file ("modelName_additional_constraints.gms") to the model declarations (schedule.gms,...).

Implementing maxFuelCons and maxFuelFraction. For main fuels, the parameters function as their names suggest; for start-up fuels, maxFuelCons is not implemented and maxFuelFraction is treated as exact fraction.

Adding ramping costs. Upward and downward ramps separated into different tiers (or 'slacks') with different costs.

Replaced q_fixedGenCap2U with q_constrainedCapMultiUnit, which enables different decommissioning and replacement decisions in addition to fixed investment ratios. Removed unnecessary parameters and divided p_groupPolicy into p_groupPolicy and p_groupPolicy3D. Renamed also the linking sets related to groups, e.g. gnu_group --> gnuGroup.

Added fixed operation and maintenance costs for investment options
Adding a new parameter unitOutputCapacityTotal to avoid division by zero
Added unit investment result parameter
Removed equation q_fixedGenCap1U
Added default value calculation for reserves update frequency
Moved tCounter update outside ms loop in 3c_periodicLoop.gms
Updated the limits of v_invest_LP and v_invest_MIP (no more maxGenCap, minGenCap)
Updated investInit_temp.gms
And some smaller updates

Model definition files included in the VCS now only include the GAMS definition (list of included equations), all of which are read by Backbone to allow for easier swapping of models without having to tamper with the "3e_solve.gms" fole. Rest of model parameters are expected to be given as input through the renamed "modelsInit.gms" in the input folder (by default). "periodicLoop.gms" and "periodicInit.gms" now treated as integral parts of the Backbone model.

Example input parameters provided by the "scheduleInit_temp.gms", "buildingInit_temp.gms" and "investInit_temp.gms" included in the defModels folder within the VCS.