Allow pausing a Princess-only game

[SJuliez]

Allows pausing the game by using Ctrl-Shift-P and unpausing with Ctrl-Alt-P.

• Both are normal keybinds that can be changed.
• It only works if only bot units remain. This limitation is artificial and can be removed but that would have little use I guess.
• This influences server packet handling so it is potentially dangerous; but as long as it isn't used I don't expect any errors from it
• The effect is purely server-side, meaning that Princess will always finish whatever she is doing which may take a while; but if things move fast, the pause happens immediately
• chat messages and log messages show pause/unpause happening

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.17%. Comparing base (a7bb1b4) to head (a58a77b).
Report is 10 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #6186      +/-   ##
============================================
- Coverage     29.17%   29.17%   -0.01%     
+ Complexity    13971    13969       -2     
============================================
  Files          2628     2628              
  Lines        266564   266581      +17     
  Branches      47575    47569       -6     
============================================
- Hits          77771    77770       -1     
- Misses       184910   184928      +18     
  Partials       3883     3883              

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