Refactor saveUnitList() to not make a new ClientGUI

[pavelbraginskiy]

Simple refactor of a previous pull request to not make the print-queue dialog depend on ClientGUI.

Also sets the default filename of the new file to the name of the original file.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.13%. Comparing base (71b9139) to head (7ed709c).
Report is 14 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##             master   #1597      +/-   ##
===========================================
- Coverage      2.13%   2.13%   -0.01%     
  Complexity      204     204              
===========================================
  Files           266     266              
  Lines         30697   30714      +17     
  Branches       5231    5235       +4     
===========================================
  Hits            656     656              
- Misses        29888   29905      +17     
  Partials        153     153              

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[HammerGS]

Conflicting files.