R1:4f0573617562

Add an icon+background selector for project images

Summary: Makes it easy to choose distinctive icons for projects.

Test Plan:
{F71018}

{F71020}

{F71019}

{F71021}

Reviewers: btrahan, chad

Reviewed By: chad

CC: chad, aran

Differential Revision: https://secure.phabricator.com/D7333