Add support for android immersive mode

This pull request is actually the same as the one I posted on the lime repo.

https://github.com/openfl/lime/pull/37

To use this change you also need the following line to your openfl project file:

    <android target-sdk-version="19" />

Tested with PiratePig ;)

![piratepig with immersive mode (navigation stuff swiped down)](https://d2oawfjgoy88bd.cloudfront.net/52c69a35888b9d0ecc34e53f/52c69b3b888b9d0ecc34e541/52f1033738d3877542c6c29a.png?Expires=1391613133&Signature=ltiePGH7PmeVgqtMHrHbDdu3pexNgpjxzcsEY6HqFVpIL3bof9prkT6fgIBYo-ffDSG8oVJNnZSSGrpofVV4esYAjqHsB5uP7Fr5Pa8PMCpaW8FH8F8VX~kDyFrj~eowbgnWGu5VGHhgmnenfB78g1ljKsT2rFm4WyVwsPK3UfAwc1gpq2UKJg0yyZzAilVcOzIFhcwfuq7kZm0i1YTMMqXa8rN3V0BJlqWLu1Sz0f1s5pfF2iV~XkdrvzGx48RbU6kfqe7uExzse1~3dNuqloHGI21PGb9FbZ8Yd4~0DxkQrO0O9yL3oWaXKw~S6gZZdct2bNBavfI-eh3KJvq0yA__&Key-Pair-Id=APKAJHEJJBIZWFB73RSA)