Full mouse support

[Cherlo]

My biggest annoyance from ONI is rotating objects.  I play the game 100% mouse only.  The workaround for building rotation is to map rotate to mouse wheel up.  This doesn't unbind zoom out, but instead performs zoom-out AND building rotation (in one direction) when you mouse up.  And also this pops up a warning at startup that there are duplication bindings.

A few suggestions to fix this. 1) By default have building rotate controlled by mouse wheel when in context.  2) Support binding of middle mouse click 3) add mod support to allow modders to build something that can do #1 or #2.