LEMS: Run example HH model

[frothga]

The LEMS backend does not correctly run the "Example Hodgkin-Huxley Cable" model.

• Outputs channelDensity, but should output channelDensityNonuniform. Need non-uniform parameter to handle surface area of segments.
• Need connections (couplings) between segments. Ensure that Coupling part is complete.

(This is an old issue found in notes on LEMS development. Need to check code and retest to verify it is still a problem.)