Ignore files with known annotation extension when loading images

[mfl28]

• Ignores files with known annotation extension (.txt, .data, .xml, .json) when loading images from a folder. The program will no longer show "Invalid image file." errors if files with these extensions are present in an image folder.
• Adds and updates test files.

Closes #67.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (ea7d111) 86.32% compared to head (6a9f3f3) 86.36%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #104      +/-   ##
============================================
+ Coverage     86.32%   86.36%   +0.04%     
- Complexity     1477     1478       +1     
============================================
  Files            95       95              
  Lines          5915     5920       +5     
  Branches        529      530       +1     
============================================
+ Hits           5106     5113       +7     
+ Misses          536      535       -1     
+ Partials        273      272       -1     

Files	Coverage Δ
...model/io/services/ImageMetaDataLoadingService.java	100.00% <100.00%> (ø)

... 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