Parental gate improvement, fixes with MutableStaticTVC and Pearl*NotificationObserver improvements.

[ADDED]     Ability to pass a title and message to the parental gate.
[FIXED]     Run beginUpdates before starting updates to activeSectionCells.
[UPDATED]   Make automaticallyAdjustInsetsForKeyboard compatible with PearlRemoveNotificationObservers.
[UPDATED]   PearlAddNotificationObserver now returns the observer.
[ADDED]     PearlRemoveNotificationObserversFrom can be used to remove observers added to non-self.