Add initial activity listing widget boilerplate
Add editor control title and icon
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
Add missing img alt-attributes
Add editor modal info section
Use static method when appropriate
Rename aktivitet-listing -> aktivitet_listing

The minus char isn't supported because when accessing widget context from
the editor template, the widget name is used ({{ widget_data.foo }}) and
the template language doesn't support the minus character.
Add method to get foreninger sorted with type data

Existing methods include only the type code, this will include their
human-readable name strings as well
Add editor controls for filtering on aktivitet organizer
Filter widget list on chosen organizer
Shorten down informational paragraph
Don't preselect in the DOM, will always be done by JS
Rehprase placeholder for required field
Add controls to filter on audiences