[DeckGL] Added fixtures and Deck test

[hughhhh]

Add utils.py for better testing examples moving that can be loaded from a json

@betodealmeida @mistercrunch

[codecov-io]

Codecov Report

Merging #4798 into master will increase coverage by 0.08%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4798      +/-   ##
==========================================
+ Coverage   72.38%   72.46%   +0.08%     
==========================================
  Files         208      208              
  Lines       15526    15530       +4     
  Branches     1203     1203              
==========================================
+ Hits        11238    11254      +16     
+ Misses       4285     4273      -12     
  Partials        3        3

Impacted Files	Coverage Δ
superset/viz.py	80.35% <100%> (+0.84%)	⬆️
...set/assets/javascripts/explore/stores/controls.jsx	38.88% <0%> (+0.86%)	⬆️

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[betodealmeida]

This is a bit fragile, and might fail depending on from which directory you run the unit tests. There's a more robust way of handling this:

1. Make sure the json files are in MANIFEST.in.
2. Make sure setup.py has the line include_package_data=True (it has).
3. You can now read the json content from using pkg_resources.resource_filename no matter where it was installed.

For 1 & 2, see this reference. For 3, see this reference.

[mistercrunch]

You could also just have the fixtures be defined as python data structures and json.dumps them if/when needed. Personally I rarely write JSON as I don't like the fact it doesn't support trailing commas and triple quoted strings.