Fix partial navigation key-combination release handling

[mfl28]

• Fixes handling of partial navigation key-combination release. Images now load correctly even if only a part of the navigation key-combination is released.
• Updates and extends unit tests.

Fixes #77 .

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.17 🎉

Comparison is base (0fcad1e) 85.93% compared to head (75371ee) 86.10%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #78      +/-   ##
============================================
+ Coverage     85.93%   86.10%   +0.17%     
- Complexity     1413     1425      +12     
============================================
  Files            92       92              
  Lines          5773     5787      +14     
  Branches        524      524              
============================================
+ Hits           4961     4983      +22     
+ Misses          551      545       -6     
+ Partials        261      259       -2     

Impacted Files	Coverage Δ
...mfl28/boundingboxeditor/controller/Controller.java	78.45% <100.00%> (+0.52%)	⬆️
...r/controller/utils/KeyCombinationEventHandler.java	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

100.0% Coverage
0.0% Duplication