Changed getManager to getManagerForClass

I've found this method today, as I was looking into a filter issue (when not using the default EntityManager, filtering on relations did not work, as the entity was not in the configured chain). 

This should fix all Doctrine ORM entitymanager problems. Also removed the getEntityManager function in the BaseController, I could not find any piece of code that uses it.

```
Changed the EntityManager for Doctrine ORM to getManagerForClass to make the code better understandable.

Removed the getEntityManager() function from the ORM BaseController, as it appears not to be used anywhere in the code.
```