front/core: Unzip textures to user dir, remove AE core customization.

Hi-res textures are now unpacked to the persistent user directory where
gamesaves/slotsaves/sramdata are saved. That way it doesn't get deleted
whenever the assets are updated. Also allows unpacked hi-res data to be
shared between several mupen-ae builds on the same device.

In the process I was able to remove another AE-specific customization
of the upstream core.

Feature requested:
http://www.paulscode.com/forum/index.php?topic=1324.0

Related commits:
0810a2252db5a06ecf0602dce0478add5eedd162
48e94450531fe6af307737cb3606b492e188d569