Adventures: more styling and UX

[rorysaur]

• Sort projects on Browse page by last updated, and style the project links a bit
• Style markdown components (mostly spacing/positioning tweaks)
• For create/edit, validate all fields on save
• (Unrelated fix) Make navbar logo link to the home URL, not just the app title

[rorysaur]

Maybe don't merge this till I look into why the success alert failed to appear while I was demoing today..