Move Wizard widget setup to .ui files

This is not exactly complete since Wizard seems to also setup Topbar
and Sidebar widgets. Hopefully we can remove that as part of a similar
change to those classes soon.
Move Topbar widget setup to .ui files
Move DisplayToolbar UI setup to UI file

In this case, there is no real advantage (we actually add a few more
LOC to the class than we remove) but this change will later allow us to
create the toolbars in other UI files directly. Besides its good to be
consistent.
Topbar itself creates/setup its display toolbar
Move DisplayToolbar into seperate file

Its not private to DisplayPage class anymore.