Add docs for sequence track, variant track, launching synteny from dotplot, and add UCSC plugin to demo

[cmdcolin]

Fixes #1479

• Adds docs for variant track sidebar sample filters
• Adds docs for sequence track
• Adds a little screenshot to features page, sometimes text heavy stuff is too much
• Adds UCSC API plugin to config
• Moves monorepo code organization to contributing

[codecov]

Codecov Report

Merging #1558 (408ea60) into master (9b27355) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1558      +/-   ##
==========================================
+ Coverage   59.50%   59.51%   +0.01%     
==========================================
  Files         435      435              
  Lines       19556    19556              
  Branches     4561     4561              
==========================================
+ Hits        11636    11638       +2     
+ Misses       7626     7624       -2     
  Partials      294      294              

Impacted Files	Coverage Δ
...inearGenomeView/components/RefNameAutocomplete.tsx	89.65% <0.00%> (+3.44%)	⬆️

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