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

In order to do that some parts has been refactored out in own templates.

Advances #73

- Use new template for cancellation badge (badge.html)
- Show more details like comment or specific cancellation types
- Fix some rules in substitution templates
- Fix cycle mechanism in substitutions_print.html

- Refactor build_timetable to return data for a single day
- Use lazy model imports
- Refactor lessons_col.html