Update to work with Nengo API changes

Updated the GUI to work with all changes up to this point: https://github.com/ctn-waterloo/nengo/commit/dd63c9bb5e4dddd4d07a469bd4076aba8b08ee70 (`decouple_api3`), where everything is a hierarchical Network, and probes work slightly different. Also made the automatic labelling better for external Networks (e.g. Ensemble Arrays).

See 7adec0f to ignore #1 and #2 in this diff.