don't use colorkey for land spray
this fixes
issue #220
rename ifTransparent to ifColorKey
This should make the name less confusing.
However this image-flag will possibly be dropped completely.
currently irrelevant sdl call adjustment
as suggested by https://wiki.libsdl.org/MigrationGuide
Change graves of teams in missions for greater variety
In A Space Adventure, only one grave was used for all teams, which was clearly bad.