Extracted existing parallel state logic from ui-view to functions in a parallelSupport object
Changed view.parallel from a state name to an array of state names.
Migrated parallel state logic from uiView to $parallelState service.  Switched "view restore" logic from reuse viewLocals to pulling from a $parallelState "Inactive states locals cache" and hooking up in transitionTo.
Registered parallel states during $stateProvider.registerState().  Moved $parallelStateProvider to state.js.  Removed parallel data from view object (now stored in the parallelState provider).  Changed getParallelStateStack to build stack on the fly from parallelState registry.
Implemented state.onReactivate and onInactivate callbacks.