properties: Make buttons vertically centered

https://bugzilla.gnome.org/show_bug.cgi?id=707296
topbar: Make buttons vertically centered

https://bugzilla.gnome.org/show_bug.cgi?id=707296
selectionbar: Make buttons vertically centered

https://bugzilla.gnome.org/show_bug.cgi?id=707296
wizard: Make buttons vertically centered

https://bugzilla.gnome.org/show_bug.cgi?id=707296