Set up istanbul with codeclimate and travis.

[bkyryliuk]

Set of changes:

• Code climate repo token is moved to the repository settings. This allows forks to have test coverage too. More here: https://docs.travis-ci.com/user/environment-variables/#Defining-Variables-in-Repository-Settings
• upgraded npm on the travis to be 3.9.5 and installed manually node v 5.11 on the travis to allow test to pass. Error message was ``jsdom 7.x onward only works on Node.js 4 or newer: https://github.com/t`. More logs are here: https://travis-ci.org/bkyryliuk/caravel/jobs/156381431
• Configured istanbul to run on the javascripts folder. There are couple limitations:
• * include-all-sources flag enforces the tool to process recursively all js and jsx files in the root directory (./javascripts). Because of it we should avoid placing libraries and generated code into that directory as it will drastically slow down the code analysis or will lead node to run out of the memory.
• Fixed the npm test command the test helper file.
• Added babel-cli to run the istanbul command.
• Added codeclimate-test-reporter package to report the stats to the codeclimate.
• Fixed couple linting errors that were failing the build.

Open issues:

• codeclimate picks up the coverage data for the default branch and I couldn't make it working for the PRs yet. Waiting for the support to get back to me.
• codeclimate report script isn't picking up the travis env variable. The hack around it is to include the token in the command.

[mistercrunch]

Awesome, thanks for digging deep into this!

[mistercrunch]

LGTM

[bkyryliuk]

Thanks @mistercrunch for the review.
There are 2 issues that have to be resolved, I'll tackled them separately: #1022

[ascott]

🎉