Add `-swc` option to export NeuroML cell files to SWC format

[sanjayankur31]

This is already implemented in the pyneuroml.swc package, so it just just needs to be exposed.

[YBCS]

@sanjayankur31 is this still open ?

[pgleeson]

@YBCS Yes, I believe it is.

[YBCS]

@pgleeson can I work on this

[sanjayankur31]

Great, I've assigned it to you now.

[YBCS]

Hi @sanjayankur31 , I am getting this error, do you have any idea what is going on here ?

I am using a virtual env
in my terminal if I simply start a python REPL and run
import lems.model.model as lems_model
import lems
there is no error but if I run the command python pyneuroml/pynml.py, then the error comes up
Is it conflicting with pyneuroml/lems.