UFO:Alien Invasion Code

* Reduced filesize of the hud pictures folder by conversion of some of the .pngs to 4/8bit-16/256 indexed colors and compressing/optimizing the .png files with pngout afterwards

* convert tga into png to reduce

* Changed png to tga after request by mattn (faster loading)
* TODO: does the transp. look ok in battlescape?

* Added new - more neutral - firemode images.

* Added Firemdoe picture fro later usage .. it's a draft, just so we have something for the list.