vertical nav: show corporation title in collection groups in the vertical navigation.

For example: Let all corporations have a status group 'foo'. Then, let another group,
called collection group, e.g. 'all foos', have all foo groups as children.
Now, they don't show as 'foo' in the vertical nav when viewing the collection group,
but they show up as 'foo (corporation name)'.
When viewing within the context of the corporation, they show up as 'foo' as usual.

Trello: https://trello.com/c/iGdAIonm/655-alle-verstorbenen-wingolfiten