Convert all the db tables into the utf8mb4 charset and use it for MySQL connections

[zenovich]

1. Convert all the db tables into the utf8mb4 charset
2. Test that emojis are supported everywhere we insert/modify character data in the db

Fixes #1176

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (96f4673) to head (e9ad00f).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1254   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          247       247           
  Lines        15283     15286    +3     
=========================================
+ Hits         15283     15286    +3     

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