actions: bug fix in lambdas in checkBan, because getBansMerged could return None (purge resp. asynchronous addBan), make the logic all around more stable;
test cases: extended with test to check action together with database functionality (ex.: to verify lambdas in checkBan);
database: getBansMerged should work within lock, using reentrant lock (cause call of getBans inside of getBansMerged);