Explicitly Order FilmBox Images By Name

[vela1606]

Fixes #1737

Checklist

• The pull request branch is in sync with the latest commit on the fo-dicom/development branch
• [n/a] I have updated API documentation
• [n/a] I have included unit tests
• [n/a] I have updated the change log
• [n/a] I am listed in the CONTRIBUTORS file

Changes proposed in this pull request:

• Explicitly Alphabetically Order FilmBox Images

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 76.46%. Comparing base (e01ca09) to head (204f7fe).

Additional details and impacted files

@@               Coverage Diff               @@
##           development    #1738      +/-   ##
===============================================
+ Coverage        76.42%   76.46%   +0.04%     
===============================================
  Files              275      275              
  Lines            25401    25401              
  Branches          3043     3043              
===============================================
+ Hits             19412    19423      +11     
+ Misses            5061     5050      -11     
  Partials           928      928              

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[gofal]

Thanks for the PR, @vela1606
Sorting the images by filename is far better than loading them in any random order that the operating system delivers.
But still it might not be right. Wouldn't it be better, first to load all the imageboxes, and then sort them by actual DICOM-tags like SeriesInstanceUID, InstanceNumber or AcquisitoinDateTime?