[cmake] adds static analysis target

also cleans up a few duplicate/mismatch source entries
Merge pull request #52 from renemilk/analyze

[cmake] adds static analysis target
fix some clang warnings & update lsl
fix clang warning
fix compile warning
get list of all spring versions
enable autoswitch of engine version when available
ask if engine should be downloaded / add hacks for comparing engine versions:

see https://github.com/spring/LobbyProtocol/issues/14
update pr-downloader: don't overwrite files when extracting