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.jade

@@ -0,0 +1,21 @@
+//-
+  XXX This template can't be transformed into a component because it is
+  included by iron-router. That's a bug.
+  See https://github.com/peerlibrary/meteor-blaze-components/issues/44
+template(name="boards")
+  +boardList
+
+template(name="boardList")
+  if boards
+    ul.board-list.clearfix
+      each boards
+        li(class="{{#if isStarred}}starred{{/if}}" class=colorClass)
+          a.js-open-board(href="{{ pathFor route='Board' boardId=_id }}")
+            span.details
+              span.board-list-item-name= title
+              i.fa.fa-star-o.js-star-board(
+                class="{{#if isStarred}}is-star-active{{/if}}"
+                title="{{_ 'star-board-title'}}")
+  else
+    p.quiet {{_ 'no-boards'}}
+    button.js-add-board {{_ 'add-board'}}