Support for yolo instance-segmentation polygon format

[m2key1]

Implemented functionality to enable the saving and loading of polygons in YOLO format (as described here)

[mfl28]

Ref #124.

[codecov]

Codecov Report

Attention: Patch coverage is 82.95455% with 15 lines in your changes missing coverage. Please review.

Project coverage is 86.45%. Comparing base (9ff6ea9) to head (298ee4a).

Files	Patch %	Lines
...8/boundingboxeditor/model/io/YOLOLoadStrategy.java	86.66%	0 Missing and 8 partials ⚠️
...8/boundingboxeditor/model/io/YOLOSaveStrategy.java	75.00%	3 Missing and 4 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #119      +/-   ##
============================================
+ Coverage     86.44%   86.45%   +0.01%     
- Complexity     1491     1498       +7     
============================================
  Files            96       96              
  Lines          5974     5986      +12     
  Branches        544      549       +5     
============================================
+ Hits           5164     5175      +11     
- Misses          531      533       +2     
+ Partials        279      278       -1     

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