Fixes

Created by: nick87720z

• I found workaround, how to get normal gtk scroll direction, like up/down instead of smooth. Without it mouse scroll will not work, probably, for any external plugin, embedded via gtkplug/socket tech (thanks to xfce-dev people).
• Styles, applied to Gtk.MenuBar objects, must also remove shadow, if any goes from current gtk style (in Minwaita it is).

p.s. Commit list there duplicates all commits from previous PR :/