Refresh players after group event

[andrewsayre]

Description:

Ensures that players are refreshed after groups change so that group_id and any other attributes are updated (only if players have been loaded.)

Related issue (if applicable): fixes #86

Checklist:

• The code change is tested and works locally.
• Local tests pass. Your PR cannot be merged unless tests pass
• There is no commented out code in this PR.
• Tests have been added/updated. No exclusions in .coveragerc permitted.
• README.MD updated (if necessary)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.74%. Comparing base (4793483) to head (a35984d).
Report is 3 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev      #89   +/-   ##
=======================================
  Coverage   99.74%   99.74%           
=======================================
  Files          21       21           
  Lines        1969     1971    +2     
=======================================
+ Hits         1964     1966    +2     
  Misses          5        5           

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