Removed unused include from GafferScene/Options.cpp.
Fixed inaccurate comment in GafferSceneTest.CustomOptionsTest.
Removed unused variable from GafferScene::AttributeProcessor.
Added matchMultiple() function to StringAlgo.h.

This allows several space-separated patterns to be tested with one function call.
Added wildcard matching to DeleteAttributes and DeletePrimitiveVariables.
Added GafferScene.DeleteOptions node.

Fixes #965.
Prefixed options in scene globals with "option:".

For the following reasons :

- In the future we may well want to store other stuff in the globals, and having a way of distinguishing options from everything else will be essential.
- It prevents DeleteOptions nodes from being able to accidentally delete displays as well.
- It removes the need for the "not a set and not a display" filtering in the SceneInspector options section (which would need updating every time we stored anything else in the globals).

Also added an outputOutputs() method to RendererAlgo.h, so outputOptions() need only output actual options.
Refactored most of DeleteOptions into new DeleteGlobals base class.
Added DeleteOutputs node to GafferScene.
Merge pull request #970 from johnhaddon/deleteOptions

DeleteOptions and DeleteOutputs nodes