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
07f3bf8d98a3
Hedgewars.png had a resolution more than twice as high as required; also fixed some (mostly obsolete) code that also contained a typo that would cause a warning/note in clang
