ESLint test

[fabienrohrer]

We would like to detect ESLint issues.

In addition to the test, .eslintrc.json should be duplicated in this repo, and eslint has to be integrated in travis.
Adding a test in webots that .eslintrc.json and doc/.eslintrc.json are identical would be even better.

References:

• https://eslint.org/docs/user-guide/getting-started
• https://gist.github.com/ronapelbaum/ef3c3459f01b002d0d719ca205401174

[omichel]

We should postpone the resolution of this issue until we implement the subrepo: https://github.com/omichel/webots/wiki/git-subrepo

[fabienrohrer]

Indeed. Testing this in webots / Jenkins rather than webots-doc / Travis would be easier.