Common reserve demand for a group of nodes

In some cases, it makes sense to calculate the energy balance at each node (e.g., at each substation in a transmission grid) but the reserve demand should be covered over a larger zone, consisting of multiple nodes, and not at each individual node.

One option to implement this, with the current version of Backbone, would be to create a dummy reserve node and links (with controlled energy transfer, infinite capacity) from the actual electricity nodes to this dummy reserve node.

Another option is to modify the reserve equation q_resDemand so that it would apply for node groups instead of individual nodes, see for example q_inertiaMin.

Changes might be needed also for q_resDemandLargestInfeedUnit.