Google-specific references hard-coded in site generator

[rofrankel]

There are a few Google-specific hard-coded things in the site generator; these make it necessary to fork the site generator in order to adopt AIPs outside of Google:

• "Google's API design decisions" in the welcome section of the main page.
• Google Analytics tracking stuff presumably specific to Google.
• The logo (mentioned here for completeness; I already filed Make logo come from AIP content repo rather than site generator #65 about this)

I'm not sure this is exhaustive, but it's what I've identified so far.