Added wolfenstein and doom sounds and songs.

Wolfenstein music: https://www.youtube.com/watch?v=AU8P43nh9Yg
Doom sounds: http://www.wolfensteingoodies.com/archives/olddoom/music.htm
Wolfenstein sounds: http://forum.blockland.us/index.php?topic=190586.0
Sequential level loading.
Optimized Texture Loader.
Bugfixes on level control.
Added Splash screens support.
Splash screens now show.
Fixed broken camera after reworking the whole rendering part.
Title, Game Over and How to Play screens.
Fixed enemy lookat.