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/cards/minicard.js

@@ -0,0 +1,14 @@
+// Template.cards.events({
+//   'click .member': Popup.open('cardMember')
+// });
+
+
+BlazeComponent.extendComponent({
+  template: function() {
+    return 'minicard';
+  },
+
+  isSelected: function() {
+    return Session.equals('currentCard', this.currentData()._id);
+  }
+}).register('minicard');