Remove TagDefs - defining tags in .model is not on the table right now
Tags are always MatrixTransforms. Closes #1951.
Merge remote-tracking branch 'robn/sgmodel-renderer-everywhere' into copy-constructors

Conflicts:
	src/scenegraph/Loader.cpp
Add copy constructors to scenegraph nodes
Add Clone method to all node classes
delete a load of unused animation time control code

Models and animations need some reworking anyway to separate per-model data
(meshes, materials, animation hierarchy, keyframes) from per-instance data
(pattern/decal/label/effect state, animation state, cached transforms).
Reworking stuff is usually easier when there's less stuff to rework, so
therefore deleting stuff is good (right?)
Delete modelviewer on shutdown
Merge remote-tracking branch 'jpab/sgmodel-animation' into sg-copying

Conflicts:
	src/scenegraph/Loader.cpp
	src/scenegraph/Model.h
Fix a ColorMap leak
Model::MakeInstance, WIP
Copy animations to model instance
Update model instance color parameters
Merge remote-tracking branch 'origin/master' into sg-copying
Move white/transparent texture to TextureBuilder, use model instance in intro
silence initialisation order warnings
Merge branch 'master' into sg-copying
Merge branch 'sg-copying'