Finish scl-lib integration

[danyill]

Add scl-lib will ensure adequate overall test coverage.

There's a bit more to do here.

Also we don't want deleting of supervisions to only sometimes remove the LN.

[danyill]

removeSupervision is now merged allowing LN or Val removal.

[danyill]

The main missing item is associated with creating new supervision LNs with no Val element.

For others which would be useful, see:

OpenEnergyTools/scl-lib#79
OpenEnergyTools/scl-lib#80
OpenEnergyTools/scl-lib#83

I don't think this is necessary for the first release of this plugin, so I'll de-milestone it.