okay, it is working now, so commit

Commit and then start messing around to break things and see what you
did to only make one side of the cube transforms display, or something
like that.
I think I got it; it was a radians issue

I didn't #define GLM_FORCE_RADIANS in the camera file, so I suspect that
the rotation got screwed up.

Cross your fingers and hope things keep working.
updated mouse tracking to always happen

By setting the Qt widget's mouse tracking to "true", I no longer have to
click to start mouse tracking.
now with vertical camera movement
made camera rotation a bit more readable
added a "mouse pressed" event

I discovered how to add a "mouse pressed" (same as "clicked", but I
guess the Qt people settled on "pressed" because maybe "click" had a
different connotation) event, but I'm not sure what to do with it yet.
now with cube rotation when clicking!

I used a couple of hashed-together globals and mouse tracking to make it
so that the camera does not move but a cube is rotated when the mouse is
click, and the camera moves but nothing rotates when the mouse is not
clicked.

What fun!
removed some duplicate code