Tabbed UI Polish Pass

[pavelbraginskiy]

Lots of small fixes and QOL improvements:

• Ensure that renaming a unit renames its tab, even after switching unit type.
• Only show the "Are you sure" prompt for operations where it makes sense, i.e. not loading a unit in a new tab.
• Fix "Load from file" not working from the startup GUI.
• Allow you to close tabs by middle-clicking them.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 2.13%. Comparing base (a493832) to head (9205ab7).
Report is 12 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##             master   #1697      +/-   ##
===========================================
- Coverage      2.13%   2.13%   -0.01%     
  Complexity      209     209              
===========================================
  Files           271     271              
  Lines         31380   31409      +29     
  Branches       5341    5342       +1     
===========================================
  Hits            670     670              
- Misses        30553   30582      +29     
  Partials        157     157              

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[Sleet01]

LGTM