osd: flatter troughs for OSD

https://bugzilla.gnome.org/show_bug.cgi?id=723829
osd: fix insensitive buttons

https://bugzilla.gnome.org/show_bug.cgi?id=723829
Theming support for popover menus

This makes popovers that are populated from menu models
look nice and menu-like.

https://bugzilla.gnome.org/show_bug.cgi?id=723014
Restrict menubutton styling

For menu buttons, we create an active state that makes the button
appear attached to the menu. That does not look so hot when the
button is actually popping up something else. GTK+ introduced
a style class, 'menu-button', to differentiate the case of a
button with a menu. Use it.

https://bugzilla.gnome.org/show_bug.cgi?id=723878
Merge branch 'osd-tweaks'
Provide a text color for plain model buttons

Otherwise, we might inherit an unsuitable one.
See https://bugzilla.gnome.org/show_bug.cgi?id=723963
popovers: fine tune

- make sure it works for dark variant
- tone down the dropshadow
- use selection blue for items
gedit: rework doc list sidpane style

https://bugzilla.gnome.org/show_bug.cgi?id=723920
suggested button: insensitive state shared with normal buttons

https://bugzilla.gnome.org/show_bug.cgi?id=722790
suggested action button: backdrop label

- remove blue dropshadow
- color label properly
gedit: documents-panel style changes

https://bugzilla.gnome.org/show_bug.cgi?id=724140
gedit: statusbar top border
Enable window dragging on toolbar separators
3.11.90