Refactor activity-listing -> aktivitet-listing
Remove unused styles
Reorder LESS hierarchy according to DOM
Implement aktivitet-listing
Perform the lookup explicitly, don't use the util filter

The utility filter is tailored for the filter form on the public search
page, and when we're adding new fields it doesn't make sense to have to
use the input field keys explicitly in unrelated code - better to just
use the ORM filters manually.
Filter widget listing on future aktiviteter
Add z-index to the positioned category