Create overview page
Link in admin AKOwner list and in change view, showing the number of AKs by user
This implements #207

Add or complete docstrings
Remove code smells
Disable irrelevant warnings
Update translations to changed line numbers and line breaks
Move duplicated code for event field pre-population and event timezone adaption to mixins

This implements #175

Move AKModel views into several subfiles to improve overview and resolve problems with circular imports
Introduce new modular status page handling (widgets and views)
Port main status page to new structure
Move AK messages status page visualization to AKSubmission (therefore, they automatically do not show up when there is no possibility to create them)
Introduce status widget for virtual rooms
Fix timezone issue for rendering of AK messages on status page
Adapt status page URL in several views and tests