Closes #84

availabilities in AK submission
availabilities in AK wish submission

work with new unique_together
instead of unique property

associate AKTrack with an Event
associate AKCategory with an Event
restrict AK requirements to those associated with the same event
restrict AK categories to those associated with the same event

truncate before numbering
remove debug print statements

add default slot size to Event model
set initial form value to event deafult slot size

if ': ' cut off starting there
if ' - ' cut off starting there
if ' (' cut off starting there
cut to appropriate length

Only change appearance of owner field for normal submission but not for wishes (since they don't have owners)

Add base url field to event
Generate Wiki link from title and base url

Improve blank and unique constraints of model:
- allow blank starting times of slotes to store durations before scheduling and adapt string representation
- change unique constraint from name and shortname of AK to unique for each event only
Implement handling of tags for submission and update (auto-creation) by using a semicolon-separated text file instead of multiple choice field
Implement handling of durations for submission
Automatically generate short name
Use different forms for submission and update
Use special adapted template for AK updates instead of submission template
Fix EventSlugMixin for POST requests

Add choosen-js library and assets for nicer looking multiple select
Add new blocks for loading of individual assets to base template
Use choosen-js for multiple fields in AK submission view

currently only works when creating a new owner

create template for AK wish submission
create form for AK wish submission
create view for AK wish submission
adapt urls and buttons

Add TODOs for other data manipulation/auto-creation/...-tasks

exclude interest
exclude track

create form class
create template
configur urls
create submission view