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/components/boards/boardArchive.js

@@ -1,8 +1,8 @@
 Template.headerTitle.events({
-  'click .js-open-archived-board': function() {
-    Modal.open('archivedBoards')
-  }
-})
+  'click .js-open-archived-board'() {
+    Modal.open('archivedBoards');
+  },
+});
 
 BlazeComponent.extendComponent({
   template() {
@@ -10,26 +10,26 @@ BlazeComponent.extendComponent({
   },
 
   onCreated() {
-    this.subscribe('archivedBoards')
+    this.subscribe('archivedBoards');
   },
 
   archivedBoards() {
     return Boards.find({ archived: true }, {
-      sort: ['title']
-    })
+      sort: ['title'],
+    });
   },
 
   events() {
     return [{
-      'click .js-restore-board': function() {
-        let boardId = this.currentData()._id
+      'click .js-restore-board'() {
+        const boardId = this.currentData()._id;
         Boards.update(boardId, {
           $set: {
-            archived: false
-          }
-        })
-        Utils.goBoardId(boardId)
-      }
-    }]
+            archived: false,
+          },
+        });
+        Utils.goBoardId(boardId);
+      },
+    }];
   },
-}).register('archivedBoards')
+}).register('archivedBoards');