- Now expects UINavigationControllers to be presented
- The only view controller to add it's own done buttons now is the hierarchy screen because it needs to pass data back to the explorer upon dismissal
- Automatically adds a Done button to the navigationItem of the topViewController of presented navigation controllers if a button is not already present
- Remove FLEXGlobalsTableViewControllerDelegate, etc, and like methods
- Adopt iOS 13 APIs for detecting modal sheet dismissal by dragging
Removes duplicate code related to presenting a view controller from the
FLEX window (usually triggered by a toolbar button).
This adds `-[FLEXExplorerViewController
presentOrDismissViewControllerFromToolbar:shouldDismiss:completion:]`
which also makes it easier for others to add their own toolbar buttons
to present some other kind of screen, or for FLEX itself to utilize
again in the future.