[pve-devel] small gui enhancment regarding dialog windows

[Thomas Lamprecht]

The problem that one cannot see any difference between a CT and a VM in the tree
with an open dialog window is not big but I need that often when testing and I
do not like it if a pop up window renders everything else useless.

The missing top border on a dialog window was also noticed by wolfgang b.,
a pop up window should have a border.

The changes are visually quite small thus a screenshot with hints here:
http://imgur.com/a/LxhZC

The background is clearly grayed out while not hiding any information.