Added Gaffer.NodeAlgo.applyUserDefaults()

Nodes created via the NodeMenu apply default values to their plugs, using the "userDefault" key in the Metadata.

Fixes #1038.
added gil release to GafferScene.matchingPaths python binding
Merge pull request #1046 from davidsminor/selectAffectedObjectsFix

Fixed hang while selecting filtered objects on a node
Exposed the DispatcherWindow to the public API.

Added acquire() and get/setDispatcher() methods. Removed dispatcher(), but that shouldn't be a compatibility break because it wasn't public until now.
DispatcherWindow.acquire() is now per-application
Merge pull request #1045 from andrewkaufman/plugConfig

Added Gaffer.NodeAlgo.applyUserDefaults()
Merge pull request #1033 from andrewkaufman/exposeDispatcherWindow

Exposing access to the DispatcherWindow for a given script.