Worchestic

Full Changelog:

This allows some outputs in a MatrixGroup not to have a target for certain signal sets, this is useful in for instance a multi-head KVM in there are signal head source PCs. None can be added to the sources list in the group to indicate any 'holes' in the list but they are not considered 'companions'.

**Full Changelog**: https://github.com/rgammans/worchestic/compare/v0.2.4...v0.2.5

**Full Changelog**: https://github.com/rgammans/worchestic/compare/v0.2.3...v0.2.4

Add availble() method to MatrixGroup

Add replug_input() method to Matrix

Api updates
- Add get_output() method to MatrixGroup
- Expose the _source attribute on an output
- Ensure MatrixOutput.select() is always called when changing the output.