Moved Transparent Color button from StatusBar to ContextBar

Of note created Selection context box for future use, e.g. selection operations (inverse, deselect, etc) or whatever.

Put Transparent Color in UISettingsImpl global section.  If this isn't a good place, perhaps a new sub settings class, similar to Tool or Pen settings.  Actually, a Selection settings class sounds like it could come in handy.

A lot of slogging through the code for this one, and sorry if I'm being presumptuous in kicking the architecture around a little bit with this change.