Move iOS event dispatcher from platform plugin to platform support.

Move iOS event dispatcher from platform plugin to platform support, so
that it can be used by multiple iOS platform plugins.

Change-Id: I9041b2de5e00e5fe8f30af2dfd922b4f5c594802
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>
Correct implementation of nested runloop to match UIApplicationMain()

The previous implementation of the nested runloop was derived from the
Mac Cocoa implementation(?), and did not correctly deal with UI
animations and other UIKit functions which are run in a different mode
to the default mode. This version corrects that (in most cases) and
switches the implementation to use CoreFoundation instead of NextStep
APIs.

Change-Id: I45802d22044465749a1e5b6207d745268f6ae8a1
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>