Use PyNML to create summaries of channel models

[gsarma]

See the examples given in muscle_model:
https://github.com/openworm/muscle_model/blob/master/NeuroML2/channel_summary/
which is generated by this script:
https://github.com/openworm/muscle_model/blob/master/NeuroML2/analyse_all.sh

Related issues: #1 , #7

[pgleeson]

In progress here: https://github.com/openworm/ChannelWorm2/tree/pg_tests/NML2_models/channel_summary