Add perun initialization to DB Manager

- remove perun,perunBl from DBManagers
- remove session from DBManagerBl and DBManagerImpl (not needed)
- remove unused imports in DBManagers
- add actual version of DB to DBManagerEntry
- add method isDBVersionUpToDate to DBManagers
- add init method to DBManagerBlImpl
- change pom to respect dependencies on DatabaseManagerBl
- fix messages in exceptions in DatabaseManagerEntry
- all managers depend now on DatabaseManagerBl
- throw an exception during initialization if DB is not actual