Support automatic resize [Part 3/4]: ui.js

* Added a resize request (setDesktopSize) triggered when connecting and by
  changes to the browser window's size.
* Hid the view-drag-hand when the display area is the same or smaller than the
  remote session size.
* Added a setting for the automatic resize feature.
* Updated vnc.html and vnc_auto.html to reflect the changes to the UI.