Fixed shader edit bug with SceneProcedural

SceneProcedural was changing the names of locations with children, which was confusing interactive renders. Now it aint.
Merge pull request #908 from davidsminor/shaderEditFix

Fixed shader edit bug with SceneProcedural
Fixed unnecessary test failure in RenderManLightTest.

It was broken by 0602be75a59fa0ef901953bb03f04ba039dbd834, where ExecutableRender stopped saving the script and instead deferred to Dispatchers.

Also removed outdated comment.
Added OpDialogue preExecuteSignal() and postExecuteSignal().
Added OpDialogue.parameterisedHolder() method.

This may be used to edit the parameter values.
Reordered GafferUI.Window methods.

There was private implementation stuff right in the middle of the public API.
Merge pull request #910 from johnhaddon/opDialogueCustomisationHooks

OpDialogue customisation hooks