UI: new module; added Beard namespace imports.
Client::Unit: updated UI references; added simple cline handler.
UI: added TabbedContainer widget.
UI: added Grid widget.
UI: added ObjectView widget and prelude basic prop object sub-view.
Client::Unit: switched viewc to UI::TabbedContainer, added test object view.
UI::Grid: removed Column guts.¹

1: The commit that added Grid was incomplete.