Add separate about page, editable in admin interface

[lkeegan]

• backend
  • add about_md to Settings
• frontend
  • add About page
  • render about_md markdown using showdown to convert to html and github-markdown-css for styling
  • add text box to edit about_md in admin settings
  • refactor shared Jumbotron code into HeadingComponent
  • refactor settings api call into a settings store
• resolves add separate about page #55
• resolves Add Readme #34

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.13%. Comparing base (4ca7c34) to head (f5572d0).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
+ Coverage   78.10%   78.13%   +0.03%     
==========================================
  Files           8        8              
  Lines         717      718       +1     
==========================================
+ Hits          560      561       +1     
  Misses        157      157              

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