Fix hard-to-read text on campaign and training page in frontend at October 31
The text was yellow against a white background (the moon in the Halloween background).
This is fixed by darkening the critical area.
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
