Add open settings keyboard shortcut

[mfl28]

• Adds Ctrl/Cmnd+, shortcut to open settings.

Closes #105.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6ddbe9b) 86.36% compared to head (a18bba7) 86.33%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #106      +/-   ##
============================================
- Coverage     86.36%   86.33%   -0.03%     
- Complexity     1478     1479       +1     
============================================
  Files            95       95              
  Lines          5920     5922       +2     
  Branches        530      530              
============================================
  Hits           5113     5113              
- Misses          535      536       +1     
- Partials        272      273       +1     

Files	Coverage Δ
...mfl28/boundingboxeditor/controller/Controller.java	78.87% <100.00%> (+0.05%)	⬆️

... and 1 file with indirect coverage changes

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[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication