Add category for expression list in skin editor.

Http/SkinEditor/app.css

@@ -63,12 +63,26 @@ body {
 	padding: 0 4px;
 	margin: 1px;
 	cursor: pointer;
+	break-before: avoid;
 }
 
 	.t-li:hover {
 		background-color: lightblue;
 	}
 
+.t-li-cat {
+	padding: 0 4px;
+	margin: 1px;
+	border-bottom: solid 1px dimgray;
+	color: dimgray;
+	font-size: small;
+}
+
+.t-li-cat-2 {
+	border-bottom-style: dashed;
+	font-size: x-small;
+}
+
 input {
 	border: none;
 	font-family: sans-serif;
@@ -286,6 +300,10 @@ input {
 	.t-li:hover {
 		background-color: darkblue;
 	}
+	.t-li-cat {
+		border-bottom-color: lightgray;
+		color: lightgray;
+	}
 	input {
 		background-color: black;
 		color: white;