clearly show that 3 legged oauth is not required (bug 866176)

* add in a clear way for a user landing on the API page to distinguish between 2 and 3 legged oauth
* give a clear example that you can copy and paste right away
I still don't think "Marketplace" reads better than "the Marketplace" does. I keep seeing people write it out like this, but I've never heard anyone say "Marketplace" aloud; it's always "the Marketplace."