UF-97 Cleanup 

I've basically done everything you've asked me for, except to provide test coverage types that are only used by the HAL POC at the moment.

- LayoutPanelPresenter
- SplitLayoutPanelPresenter
- PartManager

SelectablePanels has been removed, it was not needed anymore. 

Javadocs have been added where they've been missing. 

If you still have concerns about code quality, test coverage, etc I would still prefer if we merge it first and  improve it on that baseline. The divergence of jfuerth:0.5.x, jfuerth:UF-97 and hal:UF-97 has created a lot of headache and I think we would both benefit from a having a single, authoritative code base to develop against. IMO this should be jfuerth:0.5.x for the time being.