Semi-standardize usage of icons in many mission panels
* Question mark: Decision / user input
* Exclamation mark: Tutorial message / information
* Hedgehog: Mission introduction
* -amSkip: Mission failure
* Star: Mission success / end of game
306cedbeb213
fixed several 'retina display' images and added a bunch more (though just from upscaling the normal ones; might be nice to have 'em redrawn at a real higher resolution)