Updated GafferUI for recent IECoreGL::HitRecord API change.

The HitRecord now simply stores an integer rather than an InternedString for the name, so we use NameStateComponent to provide a mapping to names. In future, we may ditch the use of names entirely to avoid the unnecessary construction of many InternedStrings.
Added GafferSceneUI::SceneGadget class.

This contains a small OpenGL scene graph implementation which can be selectively updated based on plug dirtiness in Gaffer. This is an improvement over using IECoreGL::Renderer with GafferScene::SceneProcedural, which has to regenerate the entire scene for every Gaffer change.

This is intended to form the basis for scene viewer with improved performance.
Reimplemented SceneView using SceneGadget.

This gives a 3-20x speedup in tests where only the transform plug is being dirtied. It is of particular benefit when the objects are in the scene take significant amounts of RAM, as by only computing the new transforms we entirely avoid the cache thrashing that would otherwise occur.
Fixed SceneGadget deadlock with python expressions.

The GIL must be released on the calling thread any time the SceneGadget might evaluate the scene on a TBB worker thread, in case the node graph contains nodes which use Python.
Fixed Grid node shader assignment.

It was still using a key of "shader", but we now use "gl:surface" to differentiate OpenGL shader assignments from those for other renderers.
Reimplemented SceneView grid using SceneGadget.

This allows us to remove the annoying little WrappingProcedural class.
Removed motion blur preprocessor from SceneView.

This is no longer needed because SceneGadget ignores motion blur entirely.
Removed bloat from SceneProcedural.

It had a lot of features which were shoehorned in to support SceneView features - happily these are no longer needed now we have SceneGadget to form the basis of the SceneView.
Added todo to RenderableGadget.