[TIMOB-16495] TiAPI: Remove <fullscreen> from default tiapp.xml and deprecate in docs

I had a discussion lately on FlowDock with Tim Poulson about the <fullscreen> element in tiapp.xml and we both came to the conclusion that this element is iOS-only and does exactly the same as setting UIStatusBarHidden in the <ios> section. If this is indeed true then: - The element should be removed from the [default tiapp.xml](https://github.com/appcelerator/titanium_mobile/blob/master/support/all/tiapp.xml). - The [docs](http://docs.appcelerator.com/titanium/latest/#!/guide/tiapp.xml_and_timodule.xml_Reference-section-29004921_tiapp.xmlandtimodule.xmlReference-fullscreen) should list <fullscreen> under *Deprecated elements*.