Overview of lint errors in web interface

[Robbert]

The command line output of eslint and npm test leaves something to be desired: a good overview.

• We should try log the errors and warnings to JSON files
  • Store eslint output using for example: eslint -f json > tmp/eslint.json
• Load the tmp/eslint.json in using the new fetch() standard in a browser script
• Include lodash from somewhere in node_modules/lodash/
• Use a lodash method to group all the errors from eslint.json and show how many errors there are for each error type, sorted by number of errors

Perhaps a good place to store the output for now is tmp/, this path should already be excluded using.gitignoreandgulpfile.js`.

Best to try this in the robbert/wealth repository on BitBucket until we've got something working really well.