[keycloak-dev] Database migration support added

I've added database migration support. In summary: * JPA migration is done with Liquibase * Mongo migration is done in a similar way, but no 3rd party lib (Mongo is easier as it's schema-less and single vendor) * connectionsJpa and connectionsMongo will automatically update the database (if databaseSchema = update) For more details look at https://github.com/keycloak/keycloak/blob/master/misc/UpdatingDatabaseSch... If there's any issues let me know!