Advances #75

Resolve "Rename field "abbrev" to "short_name" (subject model, ...)"

Closes #70

See merge request !53

Close #70

Currently translated at 100.0% (113 of 113 strings)

Translation: AlekSIS/AlekSIS-App-Chronos
Translate-URL: https://translate.edugit.org/projects/aleksis/aleksis-app-chronos/de/

Resolve "Some data missing in substitutions table view"

Closes #76

See merge request !52

Include extra lessons

See merge request !51

To do that move some common parts to own template files

Include models in admin interface

See merge request AlekSIS/official/AlekSIS-App-Chronos!50

Resolve "Include header box from SchoolApps"

Closes #61

See merge request !48

Close #61

Advanced data in timetable views

Closes #72 and #73

See merge request !47

Replace ugettext_lazy by gettext_lazy. Advances AlekSIS#224

See merge request !49