Made robot 'modes'

This is a hacky/incomplete set of changes, because
   a lot of the stuff that's going to be made modal -
   specifically building things - still isn't modal.
That's because I'm going to do a separate refactoring
   of the building process.
Standardized robot modes, made building modes.

Code changes:
Instead of "get_building_tile" we have
   "get_current_click_action", which is a pretty
   hacky seeming concept, but works with our current
   UI rather well. There's a lot of hackiness sitting
   there (and in the modes) so it could use some
   cleanup at some point.
Deconstructing buildings isn't implemented yet,
   but it will be easy to do so.

In-game changes:
All actions are now the mouse button.
   (Well, except moving and mode switching.)
Rotating conveyors is now "click one while in conveyor
   building mode".
The target marker is better and color-coded.
Lasers have a (inaccurate I guess) target marker.
Merge branch 'master' of https://github.com/idupree/Lasercake

Conflicts:
	gl_data_preparation.cpp

I hackily tacked isaac's wireframe code into
   prepare_shape(). It could use some cleanup.
On the plus side, it is working properly - even the
   autorobots don't look any worse as a wireframe
   than they do as a regular polyhedron (both are
   messed up because we don't standardize the order
   of the vertices.)
fixed copy-pasto
Update Clang requirement

I built a Clang 3.1 to test with; it gave a fixable error, followed
by crashing on lots of code, which sounds familiar from last time I
tried that version of Clang on Lasercake (it worked at some code
states...).  Probably not worth supporting it.  Yell if you're stuck
on a version of Xcode with a Clang snapshot that can't quite build this
and if you can't use compilers from Macports?  Let me know if this is
a common situation.