Implement multi-selection

The UI and the internal APIs are still rough around the edges but the
feature is basically working. You can now select multiple cards and
move them together or (un|)assign them a label.

client/components/boards/boardHeader.jade

@@ -27,15 +27,43 @@ template(name="headerBoard")
           i.fa.fa-times-thin
       else
         span {{_ 'filter'}}
+
+    if currentUser.isBoardMember
+      a.board-header-btn.js-multiselection-activate(
+          title="{{#if MultiSelection.isActive}}{{_ 'filter-on-desc'}}{{/if}}"
+          class="{{#if MultiSelection.isActive}}emphasis{{/if}}")
+        i.fa.fa-check-square-o
+        if MultiSelection.isActive
+          span Multi-Selection is on
+          a.board-header-btn-close.js-multiselection-reset(title="{{_ 'filter-clear'}}")
+            i.fa.fa-times-thin
+        else
+          span Multi-Selection
+
     .separator
     a.board-header-btn.js-open-board-menu
       i.board-header-btn-icon.fa.fa-cog
 
 template(name="boardMenuPopup")
+  if currentUser.isBoardMember
+    ul.pop-over-list
+      li: a Archived elements
+      li: a.js-change-board-color Change color
+      li: a Permissions
+    hr
   ul.pop-over-list
-    li: a.js-change-board-color Change color
     li: a Copy this board
-    li: a Permissions
+    //-
+      XXX Language should be handled by sandstorm, but for now display a
+      language selection link in the board menu. This link is normally present
+      in the header bar that is not displayed on sandstorm.
+    if isSandstorm
+      li: a.js-change-language {{_ 'language'}}
+  unless isSandstorm
+    if currentUser.isBoardAdmin
+      hr
+      ul.pop-over-list
+        li: a Close Board…
 
 template(name="boardVisibilityList")
   ul.pop-over-list