[TIMOB-6152] iPad: Toggle popover

It would be nice if there was a way to toggle the Ti.UI.iPad.Popover. The usual usecase is that you have a button that opens the popover. If the button is clicked while the popover is visible, nothing happens, but the expected action is that the visible popover is dismissed.

Testcase

The testcase shows that if you click the button while the popover is open, nothing happens. What I would like to do is to just switch out the ".show" method with ".toggle" and then it would work as intended.

Ti.UI.backgroundColor = '#fff';

var win = Ti.UI.createWindow();

var button = Ti.UI.createButton({
	title: 'Open popover',
	width: 150,
	height: 40
})

var popover = Ti.UI.iPad.createPopover({
	height: 300,
	width: 300,
	backgroundColor: '#fff'
});

button.addEventListener('click', function() {
	popover.show({
		view: button
	});
});

win.leftNavButton = button;

win.open({
	modal: true
});

This could be easily solved by having a method on the popover object called ".toggle()", that will show the popover if it's not visible, otherwise hide it. There is a [simple way of doing this](http://stackoverflow.com/questions/2642405/dismissing-ipad-uipopovercontroller-when-barbuttonitem-is-pushed-while-its-open) on StackOverflow.