Adding more bugfixes for Zimbra 8.6
- Do not call dialogs from within a dialog, instead update the current dialog
- Use zmDialog setContent instead of DwtComposite view.getHtmlElement().innerHTML
  This allows rich updating of dialogs and enable HTML tab navigation
  fixed: https://github.com/barrydegraaff/pgp-zimlet/issues/6
  fixed: https://github.com/barrydegraaff/pgp-zimlet/issues/49
- Remove obsolete calls to dialog.clearContent();