iOS 8: Handling of portrait and hybrid portrait/landscape

I believe this fixes #3040 as well as also correctly supports Portrait-only applications.
@prollin Yep, I agree. Currently, <code>iOSGameWindow</code> overrides <code> SetSupportedOrientations</code> in a consistent manner to other platforms and this will flow on to setting the <code>iOSViewController</code>'s true supported orientations.

Setting the **initial** value of the SupportedOrientations to be all orientations was purely done to avoid an exception being raised when setting the <code>iOSGamePlatform</code> root view controller. In particular, because Default is essentially landscape, if I tried creating a portrait only app I was getting a <code>UIApplicationInvalidInterfaceOrientation</code> exception.

But remember, at this point the <code>GraphicsDeviceManager</code> typically hasn't been initialised. So setting the supported orientations in <code>iOSViewController</code> using the Info.plist is a bad idea, because these are going to be overridden by the DeviceManager later on anyway.

So in short, using all orientations is just set to be the new 'default' and will be correctly set later on by the user.