[TIMOB-8478] iOS: Add functionality to enable iPad SplitWindow component to be toggled via menu button and closed programmatically.

Titanium uses the MGSplitView library, which fails to provide some functionality that the native iOS UISplitViewController component provides - namely tapping the menu button that displays the popover should also cause it to be hidden (i.e. it should toggle). It's also handy to be able to close the popover from code, for example when tapping a menu item that changes the detail view, and therefore the focus of the app. I've added this functionality, and am submitting it as a PR on Github - this issue is meant to complement the PR. --- Reproduction steps: Apply the attached app.js file to a new Titanium Mobile project In portrait orientation, tap the master button in the toolbar With the popover displayed, tap the button again Expected result: The popover is dismissed Actual result: The popover remains visible --- Also, With the patch in place: With the popover visible, tap the 'Close popover' option in the master view table. The popover should be dismissed.