Reduce ruler rerendering

[cmdcolin]

This is a sort of intricate stringing through of observer() that ends up reducing Ruler bar re-renderings

It also makes calculateStaticBlocks not return a new object if it is unchanged, which possibly could be done more intelligently, but it is effective in it's current state in reducing the re-renders

Addresses #434

[codecov]

Codecov Report

Merging #467 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #467      +/-   ##
=========================================
+ Coverage   64.07%   64.1%   +0.03%     
=========================================
  Files         238     238              
  Lines        7752    7756       +4     
  Branches     1783    1784       +1     
=========================================
+ Hits         4967    4972       +5     
+ Misses       2559    2558       -1     
  Partials      226     226

Impacted Files	Coverage Δ
...rc/LinearGenomeView/components/LinearGenomeView.js	62.37% <ø> (ø)	⬆️
...e-view/src/LinearGenomeView/components/ScaleBar.js	100% <100%> (ø)	⬆️
...-view/src/BasicTrack/components/BlockBasedTrack.js	85.71% <100%> (ø)	⬆️
...nome-view/src/LinearGenomeView/components/Ruler.js	96.61% <100%> (+0.05%)	⬆️
...ear-genome-view/src/BasicTrack/components/Block.js	100% <100%> (ø)	⬆️
...nome-view/src/BasicTrack/components/TrackBlocks.js	71.42% <100%> (ø)	⬆️
...s/linear-genome-view/src/LinearGenomeView/index.js	90.72% <100%> (+0.18%)	⬆️
packages/core/util/index.ts	59.68% <0%> (+0.77%)	⬆️

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[cmdcolin]

Merging because the performance looks so good after merge