Add palette color cache object back to core (fix #1350)

[swederik]

We previously had a palette color cache object which stored retrieve palette color lookup tables. This was accidentally removed during the switch to the monorepo, which caused some images to stop displaying (#1350).

[codecov]

Codecov Report

Merging #1395 into master will decrease coverage by <.01%.
The diff coverage is 5.88%.

@@            Coverage Diff            @@
##           master   #1395      +/-   ##
=========================================
- Coverage   10.21%   10.2%   -0.01%     
=========================================
  Files         263     263              
  Lines        6600    6616      +16     
  Branches     1253    1258       +5     
=========================================
+ Hits          674     675       +1     
- Misses       4788    4798      +10     
- Partials     1138    1143       +5

Flag	Coverage Δ
#core	14.33% <6.25%> (-0.03%)	⬇️
#viewer	0.4% <0%> (ø)	⬆️

Impacted Files	Coverage Δ
...viewer/src/lib/localFileLoaders/dicomFileLoader.js	0% <0%> (ø)	⬆️
.../src/studies/services/wado/studyInstanceHelpers.js	2.36% <6.25%> (+0.56%)	⬆️

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