Store filter mappings to improve future update performance

[diogofcunha]

Relates to comment on #23

[codecov-io]

Codecov Report

Merging #28 into master will decrease coverage by 0.13%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
- Coverage   94.95%   94.82%   -0.14%     
==========================================
  Files          14       15       +1     
  Lines         119      116       -3     
==========================================
- Hits          113      110       -3     
  Misses          6        6

Impacted Files	Coverage Δ
src/selectors/filtering.js	100% <100%> (ø)
src/FilteringContainer.js	94.11% <100%> (-1.72%)	⬇️

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[coveralls]

Coverage decreased (-0.08%) to 92.529% when pulling aa2e426 on filtering-revamp into 55183b2 on master.