Add Pebkac app icon, 2x Tokens

Summary: Adds a new app icon, 2x Tokens for Retina pixelness.

Test Plan: Photoshop

Reviewers: epriestley, btrahan

Reviewed By: btrahan

CC: Korvin, epriestley, aran

Maniphest Tasks: T4044

Differential Revision: https://secure.phabricator.com/D7473