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).

client/config/blazeHelpers.js

@@ -1,13 +1,53 @@
-Blaze.registerHelper('currentBoard', function() {
-  var boardId = Session.get('currentBoard');
+Blaze.registerHelper('currentBoard', () => {
+  const boardId = Session.get('currentBoard');
   if (boardId) {
     return Boards.findOne(boardId);
   }
 });
 
-Blaze.registerHelper('currentCard', function() {
-  var cardId = Session.get('currentCard');
+Blaze.registerHelper('currentCard', () => {
+  const cardId = Session.get('currentCard');
   if (cardId) {
     return Cards.findOne(cardId);
   }
 });
+
+Blaze.registerHelper('getUser', (userId) => Users.findOne(userId));
+
+// XXX I believe we should compute a HTML rendered field on the server that
+// would handle markdown, emojies and user mentions. We can simply have two
+// fields, one source, and one compiled version (in HTML) and send only the
+// compiled version to most users -- who don't need to edit.
+// In the meantime, all the transformation are done on the client using the
+// Blaze API.
+const at = HTML.CharRef({html: '@', str: '@'});
+Blaze.Template.registerHelper('mentions', new Template('mentions', function() {
+  const view = this;
+  const currentBoard = Session.get('currentBoard');
+  const knowedUsers = _.map(currentBoard.members, (member) => {
+    member.username = Users.findOne(member.userId).username;
+    return member;
+  });
+  const mentionRegex = /\B@(\w*)/gi;
+  let content = Blaze.toHTML(view.templateContentBlock);
+
+  let currentMention, knowedUser, href, linkClass, linkValue, link;
+  while (Boolean(currentMention = mentionRegex.exec(content))) {
+
+    knowedUser = _.findWhere(knowedUsers, { username: currentMention[1] });
+    if (!knowedUser)
+      continue;
+
+    linkValue = [' ', at, knowedUser.username];
+    // XXX We need to convert to flow router
+    href = Router.url('Profile', { username: knowedUser.username });
+    linkClass = 'atMention';
+    if (knowedUser.userId === Meteor.userId())
+      linkClass += ' me';
+    link = HTML.A({ href, 'class': linkClass }, linkValue);
+
+    content = content.replace(currentMention[0], Blaze.toHTML(link));
+  }
+
+  return HTML.Raw(content);
+}));