Set favicon

Summary:

• Icon source: http://www.clker.com/clipart-grid-9-win-formatted.html (SVG)
• Designer: « L », http://www.clker.com/profile-72978.html
• License: public domain, as simple shape

Generated with http://realfavicongenerator.net/

Fixes T964.

Test Plan: Test with several devices

Reviewers: dereckson

Maniphest Tasks: T964

Differential Revision: https://devcentral.nasqueron.org/D591