frontend: UI widgets for GraphicsType setting

This patch adds graphics device to frontend models.

Previously user could only set DisplayType in vm popup.
This patch adds new listbox for setting GraphicsType too.

Change-Id: I4ec3e13b463e05190d05ac342e9edaf6078626cf
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1033547