Setup standard to enforce style on new code

[Gozala]

Fixes #1240

This change configures eslint on top of eslint-config-standard which is then configured to workaround following issues preventing us using from stock standard package:

1. space-infix-ops reports polymorphic functions:
   space-infix-ops reports polymorphic functions babel/babel-eslint#366
2. no-duplicate-imports rule triggered by import type:
   no-duplicate-imports rule triggered by import type statements standard/standard#599

All of the currently tracked fils are also listed under .eslintignore so that current code will not be listed until we get to reformat it.

[tschneidereit]

I'm fine with this overall, except for one major thing: I'm very strongly opposed to the "no semicolos" rule. The vast majority of existing code does use semicolons, meaning that people (including myself) use it as a visual aide when scanning code. It might well be that there are no technical reasons for not using semicolons as long as you adhere to a bunch of other rules. The same is true for, e.g., almost all whitespace, though, and doesn't mean it's a good idea.

I know that there's a substantial set of people preferring not to use semicolons, but from what I can tell they are still a significant minority.

FWIW, I generally vastly prefer a "more traditional" style such as airbnb's, but given how fruitless style discussions are, let's not engage in them where it's not needed. The semicolons thing I think is an important decision.

[paulrouget]

I agree with Till.

[Gozala]

After discussing this in the meeting we have decided to give it a try & maybe review this decision in the future.