Made ScriptWindow.menuDefinition() per-application.

An application must now be passed to ScriptWindow.menuDefinition() to get the definition specific to the application in question. This allows multiple applications to be run in the same process without fighting.
Merge pull request #365 from johnhaddon/perAppScriptWindowMenu

Made ScriptWindow.menuDefinition() per-application.
Fixed interactive display definition to account for typename prefixing change.
Merge branch 'master' of https://github.com/ImageEngine/gaffer
Changed version to 0.66.0 and updated Changes file.
Removed todo which is done already.
put a GIL release in the NumericPlug binding to avoid a lockup
Made the shader plug on GafferScene::ShaderAssignment accept plugs originating from boxes, so you can wrap them up in a box and expose the shader plug