Bug 1021496 - [Vertical] Implement bookmark app icon design from Classic Homescreen

This work is based off of Diego's work found here: https://github.com/mozilla-b2g/gaia/pull/20524

This pull request creates a GridIconRenderer function which has three ways of rendering icons: standard, clip, and favicon.

https://bugzilla.mozilla.org/show_bug.cgi?id=1021496
I'm still not used to using this newfangled syntax. I'll update it though :)