shorten code for listing authentication
remove unnecessary constant definitions
add small comment
work on release creation version checks

Compare a given version with the previous (release base) version number.
Only calculate version number if none was given.
fix old copy-paste error
fix typo from 72dcd55f2
change release table: allow date to be NULL

Fix MySQL conditions accordingly.
move release creation to a new StdlibRelease::create() method