Inject controller into assistant controller action

As discussed here:
  - https://github.com/KnpLabs/KnpRadBundle/pull/99/files#L0R29
  - https://github.com/KnpLabs/KnpRadBundle/pull/99/files#L0R31

It's a good practice to do so
Merge pull request #100 from gquemener/never-ever-overwrite-template

Inject request into assistant controller action via method argument