Integrate unit label code

[pvutov]

DannyMcGee wrote us some unit label code but left it unfinished. To use the essential parts of it, I wrote the simple PlatoonLabel class and merged the code in commit dfac763.

The original code is still in the repo, unfinished and more complicated than our current implementation. The classes can trivially be removed, but they probably have features and design improvements that we can take over. The PlatoonLabel prefab also has a lot of stuff on it that is disabled and was originally to be used by that code. We should take over what makes sense and remove the rest.

The legacy classes/files are:
BackgroundBlur.shader
UnitLabelGFXController
ButtonGFXControl
UIGFXController
HealthBar
UIState
UIColors