* update to android studio 4.1

* improve qispos logging

closes #48

* closes #7

* implement unit tests for diffGrades()

Reviewed-on: #47

Reviewed-on: #46

* recreate all launcher icons

* constraintlayout 2.0.0.rc1 -> 2.0.0

* closes #19
* update gradle wrapper to version 6.6

* fix login button action in Onboarding
* add release changelog
* update description
* use new version code scheme

* closes #42
* show a info text if no mensa menus where found
* the refresh spinner respects the selecte theme now

* disable swipe in fragment_grades

* parse grades and store them in a HashMap per semester

* get the grades url from qispos

* first step towards a working his online integration
* rework AddSubjectDialog
* activate fragment_on_login

* remove unused resources

* the app now saves all aditional subjects and lessons and loads them on start
* udpate gradle 6.4.0 -> 6.5.1
* update coroutines 1.3.7 -> 1.3.8
* update several androidx libraries

* all cache file stuff is now handled in the CacheController
* TCoRAPIController only handles API and Gson stuff

* gradle plugin 4.0.0 -> 4.0.1