Implement touch-specific menu.

guacamole/src/main/webapp/styles/client.css

@@ -255,4 +255,14 @@ textarea#eventTarget {
     opacity: 0;
 
     overflow: hidden;
+}
+
+/* Touch-specific menu */
+
+div#touchMenu {
+    display: inline-block;
+    background: black;
+    border: 1px solid silver;
+    padding: 1em;
+    opacity: 0.8;
 }