feat(android): add moveToBackground method

[m1ga]

Simple method to put your app into background: Ti.UI.Android.moveToBackground();

Current workarounds are:
using an intent

	var intent = Ti.Android.createIntent({
		action: Ti.Android.ACTION_MAIN,
		flags: Ti.Android.FLAG_ACTIVITY_NEW_TASK
	});
	intent.addCategory(Ti.Android.CATEGORY_HOME);
	Ti.Android.currentActivity.startActivity(intent);

or hyperloop.
This method will make it quicker to put your app to the background.