Improve linux GUI installer

[trappitsch]

Linux GUI uninstaller improvements.

• Deletes the executable
• Deletes the stored icon
• Deletes the uninstaller itself
• Then tries to delete the folder with rmdir, which will only succeed if it's empty at this point!

Only rm -rf used is for pyapp (which is tested for as well now).

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.76%. Comparing base (bc08b77) to head (49b5eca).
Report is 6 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #51   +/-   ##
=======================================
  Coverage   99.76%   99.76%           
=======================================
  Files          25       25           
  Lines        1707     1708    +1     
=======================================
+ Hits         1703     1704    +1     
  Misses          4        4           

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