UI improvements

* Implement visibility choice on board creation;

* Rework the board header bar. Remove links to un-implemented
features;

* Implement a board star counter (visible if the board have >2 stars);

* Define a new icon (a thin cross) to close elements;

* Remove $(document).on('mouseover') event handlers that were
basically fired hundreds of times for nothing, we now define a proper
Tracker dependency to execute jquery-ui plugin initialization only
when something has changed;

* Bug fixes related to list scrolling.

client/components/boards/boardList.js

@@ -0,0 +1,34 @@
+BlazeComponent.extendComponent({
+  template: function() {
+    return 'boardList';
+  },
+
+  boards: function() {
+    return Boards.find({}, {
+      sort: ['title']
+    });
+  },
+
+  starredBoards: function() {
+    var cursor = Boards.find({
+      _id: { $in: Meteor.user().profile.starredBoards || [] }
+    }, {
+      sort: ['title']
+    });
+    return cursor.count() === 0 ? null : cursor;
+  },
+
+  isStarred: function() {
+    var user = Meteor.user();
+    return user && user.hasStarred(this._id);
+  },
+
+  events: function() {
+    return [{
+      'click .js-star-board': function(evt) {
+        Meteor.user().toggleBoardStar(this._id);
+        evt.preventDefault();
+      }
+    }];
+  }
+}).register('boardList');