Add meta tags to display a preview for the linked page on twitter

Show full name of AK as tooltip
Scroll to current time

First part of #89
Also fix #87

Add link to room detail view in slot table
Fix location based nesting in plan

Closes #60
Add boolean flag to event
Hide plan for non-staff users when flag is set
Update translations

Closes #77
Show link button for virtual rooms
Display capacity and properties
Link in detail view (plan and table)
Update translations

Remove typo from calendar JS

availabilities in AK submission
availabilities in AK wish submission

Closes #74

Hide wall (hide button in plan, redirect when calling directly)
Show message on normal plan & hide current and next AKs
Link only a single schedule view in Dashboard but not current AKs and wall
Update translations

Add new helper property to model
Add and use template tag for color coding
Add helpfer functions for color blending (gradient and simple)
Also show timestamp of last edit in admin view
Introduce setting to control which changes will be higlighted

Move encoding to own files that can be included
Add url for linking to detail page to event encoding
Add color coding for category and track to event encoding
Introduce room hierarchy (building + room)

Introduce common base template for plan views
Move breadcrumbs to own file for easy referencing
Load common fullcalendar base files in base template
Introduce new block for other fullcalendar operations

Adapt filenames, references and URLs
Adapt settings keys
Adapt translations
Fix wrong settings keys in wall view

Add views
Add templates
Add urls
Add translations
Add three corresponding settings to central settings file
Minor: Fix typo in plan_akslot