Unify code style using Prettier and updates ESLint rules

[kamilogorek]

This PR includes:

• unified package.json file, so it's almost exactly the same as raven-js
• prettier setup with husky, so it runs for every file that's about to be commited
• used prettier options from sentry repository and extended eslint config to use eslint-config-prettier. This way prettier won't collide with any stylistic rules of eslint.

Notes:

• no manual code changes has been made in this PR
• setup and config has been done in a separate commit, and automated changes has been made in separate ones
• all tests are passing

Related raven-js PR: getsentry/sentry-javascript#1020

NOTE:
Tests on Node 0.8 and 0.10 are failing right now due to Husky not supporting them. To be resolved.

[benvinegar]

Can we use the same options as used here: https://github.com/getsentry/sentry/blob/e2e8530ffaa5c22b14ea73bed5d4f92cdadc4421/src/sentry/lint/engine.py#L184

[kamilogorek]

@MaxBittker @benvinegar used prettier options from sentry repository and extended eslint config to use eslint-config-prettier. This way prettier won't collide with any stylistic rules of eslint, see fe8a6fb. Those rules were found using their CLI https://github.com/prettier/eslint-config-prettier#cli-helper-tool

Same changes are reflected in getsentry/sentry-javascript#1020 (already merged).

Tests are still failing on 0.10 and 0.12, and it's know issue. See: #365