Prevent accidental selection of the container

When long pressing stuff in the sidebar on iOS, you can sometimes
accidentally select the container or the canvas. This results in a
broken state where the user can't interact with the session anymore.
This commit prevents this from happening.

app/styles/base.css

@@ -839,6 +839,13 @@ html {
   background-color: #313131;
   border-bottom-right-radius: 800px 600px;
   /*border-top-left-radius: 800px 600px;*/
+
+  /* If selection isn't disabled, long-pressing stuff in the sidebar
+     can accidentally select the container or the canvas. This in turn,
+     results in a broken state where the user can't interact with the
+     remote */
+  user-select: none;
+  -webkit-user-select: none;
 }
 
 #noVNC_keyboardinput {