Added RGBA label

Added RGBA-label to toolbar.
Values are currently taken from renderwidget, but the feature could be developed further to take the values from frame buffer
related to issue
https://github.com/appleseedhq/appleseed/issues/364

edit: I fixed the styling issues. There are many commits but basically just fixing intends...

About one comment. I don't think I can remove this include
#include "mainwindow/rendering/renderwidget.h"
from file
mousecoordinatestesttracker.h
Even though a would add forward declarations the program won't compile without it.
b.r
Liisa