Resolve "Make dropdown menu items in the sidebar not tabable when collapsed"

Closes #892 (closed)

resources/less/metager/parts/sidebar.less

@@ -54,6 +54,7 @@
         }
     }
     .metager-dropdown-content {
+        display: none;
         min-width: 160px;
         max-height: 0px;
         text-align: left;
@@ -115,6 +116,7 @@
         display: none;
         &:checked {
             &~.metager-dropdown-content {
+                display: initial;
                 max-height: 1000px;
                 padding: 0px 0px 0px 0px;
             }