Graphics: Reorganize code

Split video manager code into rendering device and scene manager.
Physics: Add interface for creating a debug drawer

Still using an old trick, though. Quite nasty, but the actual debug drawer
has to wait until vertex buffer classes are finished.
Graphics: Rewrite scene nodes

o Add some other tweaks to interfaces (most notably renamed
'attachToEntity' to 'setParentNode')
o Rewrite comstructors
o Rewrite VisNode: replaced mesh list with single underlying IAnimatedMeshSceneNode
Replace hrengintime implementaion

Previously used Irrlicht's timer, now uses copy of it's code
Add createYYY interfaces & other minor tweaks
Graphics: Replace mesh object with mesh name

createMeshNode(IMesh* mesh)
and related functions were replaced by
createMeshNode(const char* meshName)

I predict that it will stay like this.