Issue #155 - ES6 Test support

[A-gambit]

Solve issue #155:

Add support of es6 and react to tests and refactor them.
Also add ability to build tests bundle and run it in browser: npm run test:build

@mweststrate please review

The next step to rewrite jquery to enzyme from some tests file.

[A-gambit]

@mweststrate there is no js linter in this repository. Is it ok? I can add eslint, in my next pull.

[andykog]

Vote for eslint-config-airbnb!

[A-gambit]

@andykog @mweststrate Yep! I think about it.
Also, it will be better to add eslint to MobX and MobX-Utils, too.

[mweststrate]

Looking great so far @A-gambit! and +1 for linting :)

[A-gambit]

@mweststrate Can I merge it in v4?

[A-gambit]

@andykog @mweststrate What do you think about semicoma rule? Do we need it? In my opinion, it is important in typescript files, but what about javascript? I have already start lint feature in mobx-utils.

[andykog]

I, personally, hate missing semicolons in JS :-)

[mweststrate]

@A-gambit yes feel free to merge.
Personally, I prefer no semicolons (even in typescript) but I can live with both. same for tabs or spaces. But I have a strong preference for width = 4 ;-)

[A-gambit]

@mweststrate @andykog I will create a pull in mobx-util soon and we will discuss code style there)