ext6migrate: update vncconsole and remove java applet code

ext6migrate: update vncconsole and remove java applet code

includes the following fixes:
 * remove all code related to the old java applet vnc client
   (we do not use this anymore)
 * move static configuration to class definition
 * use Ext.ux.IFrame instead of widget.uxiframe (to be consistent)
 * change listener from show to activate (for browser refresh)
 * change deprecated autoScroll to scrollable
 * remove novnc option from openVNCViewer function,
    since we do not need this option anymore

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>