Exporter add quat rotation

Merged changes from branch by @crobi, which correctly exported the rotation for bones. His old branch was made before the newest exporter which supported multiple animations. 

A few notes from @crobi:

 - bones will not be guaranteed to have identity rotations in the rest pose anymore
 - animated bone scaling will be included
 - file size will increase, since I export position/rotation/scaling data for each keyframe (previously, the data was only included if it explicitly defined at the keyframe)
 - Note that pchange, rchange and schange are always true. This intentionally disables the (very shaky) code that tries to determine whether the user created a position/rotation/scale keyframe at that frame.
 - Note that animation keyframes in blender can have arbitrary (floating point) frame values, but the exporter has always only used integer frames when exporting animations. Therefore, we are effectively resampling the animation and the question whether there is a keyframe at a specific time is not relevant.

A few notes on exporting:

 - Still only supports one Armature
 - Select the armature and make sure it's in Pose Mode before exporting
 - Make sure Mesh is in default pose when exporting. Two ways to do this:
   1. Delete the armature modifier, export, then undo to restore the Armature.
   2. Create a T-pose animation that has mesh in base pose. This animation should be the active action when exporting.