tests: add and follow eslint rules

[come-maiz]

I copied the rules from zeppelin solidity, and added the react module. There are still a few lint errors that somebody with more knowledge about react should check.

Requires #7.

[come-maiz]

I am not in favor or against any of these rules. This is mostly to start a discussion about consistency in the js code of all our projects. I'm happy to adjust the rules and update the code if we want to choose a different set of rules.

[facuspagnuolo]

I would like to discuss these kind of rules a bit more, I'm not a big fun of being so restrictive with code styling

[eternauta1337]

@ElOpio what do you think? is this the best place to discuss this sort of thing?
If you do, please see if you can upgrade the changes to the latest master, since it has changed quite a bit in the last few days.

[come-maiz]

@ajsantander, no, the place to discuss these things is now https://github.com/ZeppelinSolutions/code-style
I've updated the branch, but please merge it next, before it diverges again and the sync becomes more complicated.
Feel free to disagree with any of the rules. We are just taking them as an initial point, so if you dislike something, please report a bug in the code-style repo and we will discuss about it after this initial one lands.