Updated theme dependencies and assets.

[AlexSkrypnyk]

• Added ahoy lint-be-fix and ahoy lint-fe-fix commands.
• Switched to Stylelint for theme linting and added npm lint-fix command.
• Simplified theme colours.
• Updated theme logos and a screenshot.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.12%. Comparing base (c83c326) to head (aaf4178).
Report is 5 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1355   +/-   ##
========================================
  Coverage    67.12%   67.12%           
========================================
  Files           41       41           
  Lines         3051     3051           
========================================
  Hits          2048     2048           
  Misses        1003     1003           

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