Particle collision 92

This adds particle collision events, handled in the collision.lua.
Collision detection is implemented in the particlecollision.cpp:
- iterate over all pairs of particle groups, check for bounding box collision (performCheck())
- call "boundingBoxCollision" in lua
- lua may call "pc_checkCollidedParticles" if desired for the collided elements
This will perform a tree based check. Please check the sources for this test =)
- call lua again, "particleCollision", so that we decide in the script what to do exactly with the relevant particles.

Adds an abstract Drawable superclass with: vao/vbo member, bounding box getter (unset per default).
"ShadowingDrawable" superclass for drawables that implement the "drawDepthMap" functions etc.

Adds an (generic) DebugStep, that may be used to render any helpful debug infos: enabled with F1. This renders the bounding boxes of all drawables that set their box (as wireframe), and the the bounding box of the collision volume (solid box), which you will probably only see if the collision test gets too slow.

Also enables the lua wrapper to send glm::vec3's to lua scripts (but not the way back, yet).

Seems too much for one pull request..