Support Ca2+ dependent K channels imported from NML

[dilawar]

Currently moose does not have very good support for channels which depends on concentration of some pools e.g. Ca2+ . Relevant discussion is here: NeuroML/NeuroML2#117

[github-actions]

Stale issue message

[dilawar]

Reopening after github bot closed it prematurely.

[dilawar]

PR #396 adds some support for this.