Improved shader assignment reporting in SceneInspector.

We now show the name of the node which generated the shader if it is available.

Fixes #335.
Improved shader handle generation.

Handles are now generated in a repeatable fashion, and include the name of the node from which the shader was generated.
Merge pull request #786 from johnhaddon/shaderHandles

Improved SceneInspector shader display and shader handles