Generate an API key for all users

This is so that we can authenticate to the API using a token always.
Introduce Spree.uri and Spree.ajax helpers

Spree.uri is just a proxy to Spree.url. I kept typing uri when I meant url, and thought people might want to do both.

Spree.ajax takes some arguments and processes the URL through Spree.url before passing it to $.ajax. This is useful for people who want to make authenticated API requests to Spree.