Implement golden tests

[chshersh]

Create .json file with the example of how the value of the example data type should be encoded in JSON and then:

• [ ] Parse file in Haskell and compare with golden value
• [ ] Encode golden Haskell value and compare with file
• [x] Parse file in Elm and compare with golden value
• [ ] Encode golden value in Elm and compare with the file content

[vrom911]

I will try to investigate testing on Elm side.