Extract all bindings and support multiple certificates when decoding idp metadata

[kmacgugan]

Extract all bindings when decoding idp metadata.

-Before, this would only look for HTTP-POST login locations. Now, it will extract any location it finds: post, redirect, or artifact. The way this is achieved is not the most beautiful, but allows for easy matching when #esaml_idp_metadata is used.

Support multiple certificates from idp metadata.

-Changes the esaml_idp_metadata record: certificate -> certificates, now of type [binary()] instead of binary(), with undefined instead of [] winning if there's nothing in the metadata xml document.

Adds okta-ish and azure test metadata.