Enforce a consistent ES6 coding style

Replace the old (and broken) jshint + jscsrc by eslint and configure
it to support some of the ES6 features.

The command `eslint` currently has one error which is a bug that was
discovered by its static analysis and should be fixed (usage of a
dead object).

server/publications/cards.js

@@ -1,4 +1,4 @@
-Meteor.publish('card', function(cardId) {
+Meteor.publish('card', (cardId) => {
   check(cardId, String);
   return Cards.find({ _id: cardId });
 });