[keycloak-dev] Database migration support added

[Stian Thorgersen]

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/UpdatingDatabaseSchema.md

If there's any issues let me know!