OpenCS settings

The Subview section is not yet implemented, but I would like people to try it out and provide feedback comments please.  There are some debug statements still in there, please ignore them ;-)

Unfortunately I couldn't make use of existing settings code by graffy76 (couldn't work out how to use the settings framework with Qt Designer generated header file)
Currently we only update the render window when its content changes, so having VSync doesn't really make sense.