Revamp ColorButton

Revamp ColorButton

Rather than requiring parent widgets using this to connect all sorts of signals and show the
color selection dialog themselves, move this into ColorButton itself, making it a
self-sufficient widget. Also, we're now using the Qt property system, and emit a
colorChanged() signal.

Oh, and we inherit from QToolButton now, which seems to be a saner choice on MacOSX and also
allows for nicer layouts on all platforms. Yes, we'll try and improve the looks later on, right
now it's just a crude QPixmap overlaying the button.