n(euro)ml->morphml as appropriate

* since we are only proposing to parse the level 1 morphml subset of neuroml
cable information is optional in neuroml
trap neuroml2 files
fix bugs due to earlier renaming
Add test data from neurml.org

* nb this is all based on the v <=1.8.1 spec not neuroml2
Test that we can read valid neurons from neuroml format
test (failure) for neuroml2

* the example comes from

https://github.com/OpenSourceBrain/CATMAIDShowcase/blob/2158565a36e44140f4172672667ae4e21d417b7c/NeuroML2/catsmall.nml