Improve re-brandability

[earth2marsh]

Similar to @rofrankel 's AIP issue , it should be easier to add custom branding when you fork AEPs. That can signal that "this is the official internal set of AEPs" for any company.

At the very least, this could be docs improvements to explain how to add a logo prefix to "AEPs" in the header, but it should also include favicon replacement instructions.