Fix issue detected while creating test

This includes a new helper method to assert the existence of a particular message

Introduce framework to simply test correct rendering of views
Create tests for dashboard views
Create tests for plan views
Create tests for default admin views (add and change) of AKModel models

Use event slug and timestamp in filename for slide export

See merge request !147

Improve scheduler

See merge request !146

Show total count of violations as number, but only mark in orange if there are any violations that are not manually resolved already

Allow AKSlot creation via scheduler

Closes #120

See merge request !145

This implements #120

Use target parent for virtual room buttons on room detail page, too

See merge request !144

Use target parent for remaining virtual room buttons on AK detail page, too

See merge request !143

Use target parent for going to virtual room buttons

See merge request !142

This ensures correct loading if AKPlan is called from within a frame, e.g., in Venueless

Fix room adding form

See merge request !140

Make sure calendar is only loaded when event was already set

Introduce view for room import from CSV

Closes #156

See merge request !139

This implements #156

Improve scheduling

Closes #93 and #159

See merge request !137

Load custom css in admin interface, too
Fix lading of locales in scheduler
Improve icon in scheduler
Reduce SQL query amount in scheduler

Create new view (including template and form)
Link on status page
Add translations

Move general ajax setup call to external js file
Move common functionality for CV loading to external js file
Visualize existing violations in scheduler
Add reloading function to scheduler