Rename event 'categories' (application_process)

Right now we have 3 possibilities for the application process for events:

1) `selection_by_travis`
2) `selection_by_organizer`
3) `application_by_organizer`

Since Travis is no longer involved in management and selection, we should rename them to sth. more general.

I suggest:

1) `listing_application_and_selection`
2) `listing_and_application`
3) `listing`