fixed sidebar menu tree dropdown always open

- added code from #2001 thanks @CoderSquirrel

Closes #1854 & #2001

build/less/treeview.less

@@ -1,4 +1,4 @@
-// Tree view menu
+	// Tree view menu
 .treeview-menu {
 	display: none;
 	list-style: none;
@@ -27,4 +27,19 @@
 	    }
 	  }
 	}
+}
+
+.treeview {
+	> ul.treeview-menu {
+		overflow: hidden;
+		height:0px;
+		padding-top:0px !important;
+		padding-bottom: 0px !important;
+	}
+}
+.treeview.menu-open {
+	> ul.treeview-menu {
+		 overflow: visible;
+  		height:auto;
+	}
 }

dist/css/AdminLTE.css

@@ -3096,6 +3096,16 @@ table.text-center th {
 .treeview-menu > li > a > .fa-angle-down {
   width: auto;
 }
+.treeview > ul.treeview-menu {
+  overflow: hidden;
+  height: 0px;
+  padding-top: 0px !important;
+  padding-bottom: 0px !important;
+}
+.treeview.menu-open > ul.treeview-menu {
+  overflow: visible;
+  height: auto;
+}
 /*
  * Page: Mailbox
  * -------------

dist/css/alt/AdminLTE-without-plugins.css

@@ -3096,6 +3096,16 @@ table.text-center th {
 .treeview-menu > li > a > .fa-angle-down {
   width: auto;
 }
+.treeview > ul.treeview-menu {
+  overflow: hidden;
+  height: 0px;
+  padding-top: 0px !important;
+  padding-bottom: 0px !important;
+}
+.treeview.menu-open > ul.treeview-menu {
+  overflow: visible;
+  height: auto;
+}
 /*
  * Page: Mailbox
  * -------------