Add the possibility to view the status of case-studies in the gui

[Sinerum]

Add a casestudie filter aswell as the ability to view the status of a case study when browsing revisions in the cast study generation gui

[codecov]

Codecov Report

Attention: Patch coverage is 19.71831% with 57 lines in your changes are missing coverage. Please review.

Project coverage is 66.38%. Comparing base (982bf9b) to head (c752ce5).

Files	Patch %	Lines
varats/varats/gui/cs_gen/case_study_generation.py	22.41%	45 Missing ⚠️
...rats/varats/gui/cs_gen/case_study_generation_ui.py	0.00%	12 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##           vara-dev     #880      +/-   ##
============================================
- Coverage     66.49%   66.38%   -0.12%     
============================================
  Files           344      344              
  Lines         27935    28002      +67     
============================================
+ Hits          18575    18588      +13     
- Misses         9360     9414      +54     

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[boehmseb]

Newer versions of PyGit2 don't support Commit.hex anymore.
This would be a good chance to fix this for the cs-gui.