Physics: Add ICollisionObject getRotation & getPosition
Physics: Update implementation of getRotation & getPosition
Physics: Rewrite quaternion to euler angles conversion

Rewritten to add singularity check.
I used formulae from
http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToEuler/
Physics: Move quaternionToEuler implementation to .cpp

It wasn't very sensible to make this an inline function.