[Core] Refactor RepositoryService to allow injecting of dependencies.

* Domain repositories are now wrappers for doctrine's document repositories.
* If there is no custom repository, a generic repository will be created.
* Do not use attribute "repositoryClass" in Document annotations any more.

(references gh-12)
[Auth] Refactor auth repository and entities to make it work with new RepositoryService

(references gh-12)
[Jobs] Refactor job repository and entities to make it work with new RepositoryService

(references gh-12)