Ability to show more then one level of subnav in the primary navigation

[occupant]

Problem:
Some units would like to display more than a single level of subnavigation in the primary navigation, but still leverage the default CLF menu styles. This is currently limited to a single level due to styling and theme options.

Proposal:
Add ability to override the single level of subnav in the primary via either theme option or instructions (e.g. using Menu block, providing a compatible template, instructions and styles).