Limit webaccess clipboard textarea min width

The clipboard textarea could potentially shrink further than what was
possible for the header text elements, which looked a bit broken. In
that regard, a min width is introduced for the textarea.

app/styles/base.css

@@ -572,6 +572,7 @@ html {
 }
 #noVNC_clipboard_text {
   width: 500px;
+  min-width: 150px;
 
   box-sizing: border-box;
   max-width: 100%;