Fix detailed progress dialog visual glitches

Before, the ProgressDialog widget was hidden under any toolview, but not by the
editor widget or any of IdealToolBar widgets. I have been unable to track down
why it doesn't work with current setup design: According to GammaRay both a
toolview (e.g. "Problems", "Find/Replace in Files") and ProgressDialog are
children of MainWindow widget, but still even manually raising and lowering from
within GammaRay didn't fix Z-order.

The workaround "hide the tool view, and activate it again (while the detailed
progress widget is shown)" actually works only for first frame, then the part
of ProgressDialog overlapping with tool view widget does not update anymore.

I fixed this by converting the OverlayWidget to a popup widget (just like
ActiveToolTip).

Also while there, I fixed removal of separator line between progress items -
depending on the Qt specific behavior as mentioned in removed comment doesn't
seem to work out (anymore?).

REVIEW: 125929

From ffce9fc57efb10b03d6b21e4fcbff40607e072d6 Mon Sep 17 00:00:00 2001
From: Maciej Cencora <m.cencora@gmail.com>
Date: Tue, 3 Nov 2015 10:45:29 +0100
Subject: [PATCH] Fix detailed progress dialog visual glitches