Proposed header change.
Merge branch 'master' of https://github.com/johnhaddon/gaffer into unsavedChanges
ScriptNode unsaved change tracking.

ScriptNode now has an "unsavedChanges" BoolPlug which is kept up to date when Actions are performed and when the script is save()d or load()ed. This will form the basis for UI elements preventing the user from accidentally losing work when closing windows or quitting. Additionally ScriptNode plug accessors now use the much faster index based accessors rather than name based lookup and unecessary member data.
ScriptWindow close icon and ApplicationMenu Quit item both now prompt the user before discarding unsaved work.
Hiding unsaved changes plug in the Settings... window.
Merge pull request #69 from johnhaddon/unsavedChanges

Prompt user when exiting would lose unsaved changes.