chore (ESLint): Add eslint + typescript + prettier support

[jamesopti]

Summary

Setup ESLint w/Typescript & React support

Autolint 2 files just to make sure it works.

Once the core code is approved, I'll autolint the entire repo in another PR.

Approach

I used the Prettier.io recommended setup with ESLint as well as this guide to help integrate Typescript.

The .prettierrc file was copied directly over from the javascript-sdk.

A few rules (3) were turned off so that after this PR, eslint --fix leaves us with no errors.

We can discuss after that if we want to turn those rules back on.

[mjc1283]

Hmm, so from the TypeScript side, the syntax we are allowed to use is a function of both the TypeScript version we use, and the compiler options (like lib, which is currently set at es2015). How do these play together? Are we forced to specify ecmaVersion here?

I am wondering if we would be better off just introducing Prettier for formatting, and leaving static checks to TypeScript for the time being. I wonder how much overlap there is between correctness checks in ESLint and the TS compiler's responsibility.

[mjc1283]

Discussed offline, there shouldn't be any interference.

[jamesopti]

Im going to set the ecmaVersion here to 2015 to match the current tsconfig lib, as you noted here!