fix build with GCC 4.6
use 'override' keyword to check/document which methods are overrides
Re-enable OpenGL thread by default

Nouveau seems to be fixed for me these days and not
have the performance problem with rendering from a separate
thread anymore.  And that was the only reason that it
wasn't enabled by default.
Improve quitting code & comments.

Now we quit via Qt's event loop.

More patch next.
Make quitting more robust.

Now we indeed close the OpenGL thread when quitting
any time that it exists and we quit.

This (hopefully) makes buggy OpenGL implementations happier.
fix comment
clean up OpenGL state
don't check for OpenGL when there's no GUI anyway
add mouse input infrastructure

clicking on the window makes it capture the cursor.
notes
Allow you to control 'robot's facing using the mouse.

TODO we should allow controlling most anything's facing this way.

This commit also fixes the main.cpp mouse infrastructure a bit.
add mouse button support as an input key
Merge branch 'master' of https://github.com/idupree/Lasercake

Conflicts:
	specific_object_types.hpp