Add map screenshots into the mod so you can see on loading screen

Brought this up about 10 times before. Need to be 2:1 ratio in power of 2 size, basically make them 512x256 or 1024x512, then upload to repo and set the path to them in your mission general settings. Needs to happen on almost all missions made in the last 2 months. This makes it a lot easier to pick the mission you want