UFO:Alien Invasion Code

* base/pics png crush.

* crushed png files

* make the mission briefing already visible at loading time and removed the loading images

* removed all the loading images - the mission briefing window is used now with a default loading image (this can be tweaked)
the work that needed to be done to get the loading images up-to-date with each render and/or map update wasn't worth the output imo
* extended the cgame api with a dedicated mission briefing callback

* Replaced the default map loading picture with a rendering made by RaXaR (after receiving e-mail confirmation from him that we can use his picture (Quote from RaXaR: "The license is free to use in whichever form you wish. Basically BSD or anything even less restricting."))
* Updated LICENSES