add interest window

See merge request !111

Additionally, remove obsolete logging

Merge branch 'interest_restriction' of gitlab.fachschaften.org:kif/akplanning into interest_restriction

This endpoint checks for validity of the request and increments the AK interest counter if currently allowed

adds datetimefield for start to Event model
adds datetimefield for start to Event model
adds translations
adds migration

Implement additional constraint validation checks

See merge request !110

Both violation and warning for capacity nearly exceeded
Adapt model (better description for capacity exceeded violation type)
Add comment to detail fields of constraint violation

As suggested in review

Fix now indicator in fullcalendar views (AKPlan) for users from other timezones

See merge request !109

This is done by generating the "now" timestamp from python instead of JavaScript using a newly created templatetag
The new "now" function is used in all AKPlan calendar views as well as in AKScheduling's scheduler view

Fix CSP for new event wizard (allow loading external style/script files for datepicker)

See merge request !108

Introduce and use a present_by_default attribute for AKCategory

See merge request !107

Use for slide generation
Show effect it will have on AK detail page
Add migration
Add translations

Change title of AK Detail Page

See merge request !106

Constraint Violation checking & visualization

See merge request !99