LL-445
* provided the possibility for services to register operations only supported up to a particular amount of client connections per user - currently set for ops entityDescsGet (1), dataImportEvernote (1), learnEpVersionGetTimelineState (10) and learnEpVersionSetTimelineState (10)
* throw error if amount of threads handling same ops for given user exceeds set limit
* throw error if amount of active database connections exceeds a certain share of set limit (i.e. maxActive from the apache db connection pool)