Add Apple Touch icon for Labs

This patch provides an Apple Touch icon for Wikimedia Labs.  It comes
as a 152x152 px square to satisfy the needs of iPad devices with the
new Retina display.  (iOS will scale the icon down if need be.)

Originally submitted as d007275f00a757cad9dd4dcc6f17bc7da68eb9de to
operations/mediawiki-config.

Bug: 52583
Change-Id: I12926f97857748317f21dfb061b644ec08984ad7
Merge "Add Apple Touch icon for Labs"