Fixes actionmenu for forwardings.

Right now all transitions are displayed as agency actions by mistake. This PR solves this problem and add missing translation for the agency-dropdown.

Renamed ForwardingTransitionController, to support the same lookup for tasks and forwardings.

Only when the name is identical, the [adapter lookup](https://github.com/4teamwork/opengever.core/blob/65af2a06b2098034e18c1bf911f1a0f620005be7/opengever/task/viewlets/actionmenu.py#L28) works correctly for forwardings too.

@lukasgraf please have a look ...