[GLES] Batch textures and their borders

Gives a considerable speedup in scenes with many bordered images
(like settings).
skip dxt compression on all arm boards

The only chipset I'm aware of that can do dxt on arm is Tegra, and that's not
worth slowing everyone else down
[GLES] clear screen (in the right place) before shutdown
fixed, hook GetPreferredResolution in WinSystemEGL