Intrusive Subsimulation Editor

[Grissess]

It would be quite nice to be able to edit subsimulations from within the editor for a given simulation, though it would require additional support from the network editor, which currently has no concept of subnetworks, and the Qt implementation's support is dubious at best. Nonetheless, the save file is XML, which can be arbitrarily self-embedded, and this would theoretically allow complex simulations to be entirely self-contained in one file, as well as linked to other files.