Fix issues in REBUS

Show class teachers on plan views

Fix problems with missing validity of forms if selecting other categories than printer issue

Add prop types and compiled rebus js to static files

Close #324 and one other issue which was unknown before

closes #331

Bugfix/offline fallback

change cache/network fetch behaviour of serviceworker.js

# Conflicts:
#	COPYRIGHT
#	README.md

# Conflicts:
#	schoolapps/dashboard/urls.py
#	schoolapps/dashboard/views.py
#	schoolapps/templates/partials/footer.html

Optimize design for dashboard (issue #321)

- Include React via babel compiler directly instead of using gulp/CRN…

Update serviceworker.js

don't cache login page

- Use production variantes of React, React DOM and Prop Types if not in debug mode (mentioned by @ZugBahnHof)

# Conflicts:
#	schoolapps/static/common/style.css

bugfix PWA caching

Merge/dashboard cache

# Conflicts:
#	.idea/misc.xml
#	requirements.txt
#	schoolapps/dashboard/urls.py
#	schoolapps/dashboard/views.py
#	schoolapps/schoolapps/settings.py
#	schoolapps/schoolapps/urls.py
#	schoolapps/templates/partials/header.html
#	schoolapps/timetable/views.py

Bump mixin-deep from 1.3.1 to 1.3.2 in /dynselect2

Bumps [mixin-deep](https://github.com/jonschlinkert/mixin-deep) from 1.3.1 to 1.3.2.
- [Release notes](https://github.com/jonschlinkert/mixin-deep/releases)
- [Commits](https://github.com/jonschlinkert/mixin-deep/compare/1.3.1...1.3.2

)

Signed-off-by: dependabot[bot] <support@github.com>

Feature/pwa optimization