Fix posttroll-based notifier for move it server

[mraspaud]

This PR fixes the mess created with the watchdog refactoring to the posttroll-based notifier.

• Closes move it server fails to start when config uses listen instead of origin #194
• Tests added

[codecov]

Codecov Report

Attention: Patch coverage is 70.37037% with 16 lines in your changes missing coverage. Please review.

Project coverage is 91.28%. Comparing base (a52ee84) to head (b67812c).
Report is 43 commits behind head on main.

Files	Patch %	Lines
trollmoves/server.py	60.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #195      +/-   ##
==========================================
+ Coverage   91.12%   91.28%   +0.15%     
==========================================
  Files          26       26              
  Lines        5421     5417       -4     
==========================================
+ Hits         4940     4945       +5     
+ Misses        481      472       -9     

Flag	Coverage Δ
unittests	91.28% <70.37%> (+0.15%)	⬆️

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[pnuu]

LGTM