Addded possibility to add dividers to System Command Menu

docs/configuration/config_yaml.rst

@@ -730,6 +730,15 @@ OctoPrint is running is allowed to do this without password entry:
        command: sudo shutdown -h now
        confirm: You are about to shutdown the system.
 
+You can also add an divider by setting action to divider like this:
+
+.. code-block:: yaml
+
+   system:
+     actions:
+     - action: divider
+
+
 .. _sec-configuration-config_yaml-temperature:
 
 Temperature

src/octoprint/templates/navbar/systemmenu.jinja2

@@ -3,5 +3,10 @@
     <b class="caret"></b>
 </a>
 <ul class="dropdown-menu" data-bind="foreach: systemActions">
+    <!-- ko ifnot: action.startsWith("divider") -->
     <li><a href="#" data-bind="click: $root.triggerAction, text: name"></a></li>
+    <!-- /ko -->
+    <!-- ko if: action.startsWith("divider") -->
+    <li class="divider" />
+    <!-- /ko -->
 </ul>