Extended UAVO widget checkbox relation to support arbitrary strings and added support for groupboxes

This was a pretty easy fix. It basically involves adding a dynamic property to the widget (setProperty is inherited from QObject, so this method is available for pretty much everything in Qt). When making the checkbox/groupbox, it is enough to define "TrueString" (with the UAVO field name representing the checked state) and "FalseString" (with the UAVO field name representing the unchecked state).

An example of how to use this is in https://github.com/TauLabs/TauLabs/pull/365/files#diff-1.

Thanks to @peabody124 for the hint about where to look.