chore: configure prettier and eslint

- add prettier to do formatting
- add eslint-config-prettier to
  disable rules conflicting with prettier
- remove eslint from grunt workflow
- use lint-stage to lint and format
  on precommit
- use eslint and prettier in travis directly
- remove rules that are already part of
  the "recommended" ruleset

That rational is that eslint and prettier should be run in
Travis-CI, on commit and as IDE integration (highlighting
errors directlry). They don't need to be run along with
test-cases. Getting linting errors when running the tests
because of missing semicolons is just annoying, but doesn't
help the overall code-quality.

integration-testing/multi-nodejs-test/.eslintrc.js

@@ -1,12 +1,13 @@
 module.exports = {
-  "extends": "eslint:recommended",
-  "globals": {
-    "self": false
+  extends: ['eslint:recommended', 'plugin:es5/no-es2015', 'prettier'],
+  globals: {
+    self: false
   },
-  "env": {
-    "node": true
+  env: {
+    node: true
   },
-  "rules": {
-    'no-console': 'off'
+  rules: {
+    'no-console': 'off',
+    'no-var': 'off'
   }
-}
+};