Add support for SAML 1 Tokens

This pull requests add support for SAML 1 Tokens. There are a couple things to note:

* I based the saml1_example.xml on the service I am communicating with, but replaced most of the values with the corresponding values in acs_example.xml
* Your comments in auth_callback.rb imply that you did not expect "audience" to vary between SAML 1 and SAML 2. I needed these to differ because SAML 1 has namespaces attached to the elements.
* I needed to make a change to xml_security.rb because the ID in the "check digests" section is named "AssertionID" instead of "ID".

Let me know if you have any feedback about how this could be improved. Thanks.
If you set `saml_version` as integer, this will not work, it would be better to `case settings[:saml_version].to_s`