Tweak pinboard styles

Summary: Curves, gradients, black and white designs. Some of those are in here.

Test Plan: Tested Macro and Pholio, better, tighter spacing. We could probably use bigger images. Checked iOS and Chrome.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4970