Propagate file action changes to the file lists

Whenever an app needs to register an event late, it does that on the
original file actions object.

Since the file actions that the file list work on is a merged list, not
the original one, the registration event needs to be propagated there as
well.

Fixes https://github.com/owncloud/core/issues/9463

Please review @icewind1991 @MorrisJobke @DeepDiver1975 

I'm not super happy about this approach, but it's the best I can do short term.