Add depth/breadth sections, fix formatting issues

@markpundsack @ebrinkman @kencjohnston

This is the first iteration on expanding on our depth and breadth sections on the direction page. I'm killing two small birds with one stone here, and linking to the epics for new categories and those we're focusing on this year. Right now, it's all written statically, but I will rewrite these sections to pull programmatically when I have a better vision of what to do with this content this week.