Default to collapsed threads

Make threads start collapsed. This is possible because it now doesn't
affect the visibility of top-level cards.

h/static/scripts/directives/thread.coffee

@@ -13,7 +13,7 @@
 ThreadController = [
   ->
     @container = null
-    @collapsed = false
+    @collapsed = true
 
     ###*
     # @ngdoc method