[web] implemented twig templating system (#4264)

Signed-off-by: Kristian Feldsam <feldsam@gmail.com>

data/web/templates/mailbox/tab-mailbox-defaults.twig

@@ -0,0 +1,10 @@
+<div role="tabpanel" class="tab-pane" id="tab-mailbox-defaults">
+  <div class="panel panel-default">
+    <div class="panel-heading">
+      {{ lang.mailbox.mailbox_defaults }}
+    </div>
+    <div class="panel-body help-block">
+      {{ lang.mailbox.mailbox_defaults_info }}
+    </div>
+  </div>
+</div>