Introducing Site Icon, favicon management for WordPress.
This v1 marries Jetpack's Site Icon module with the Media Modal, reusing code
from the Custom Header admin. For now, the core-provided icons will be limited
to a favicon, an iOS app icon, and a Windows tile icon, leaving .ico support
and additional icons to plugins to add.
Props obenland, tyxla, flixos90, jancbeck, markjaquith, scruffian.
See #16434.