I should be able to define navigation bars/menus for my Space

Summary: The details aren't entirely obvious -- it might be with top menus or sidebars -- but there should be a consistent way to define a consistent menu across the entire Space.

This is not terribly difficult, using Bootstrap. The right answer is likely a left-side navigation bar as the default, likely defined as a Model Property with sections, each of which has a title and a list of Links.