Completed SP_test refactoring
* Implemented all response builders
* Implemented minimum required metadata builder
* Added required .xsd files in order to validate the generated SAML
metadata and responses
* Finished refactoring the sp_test.client module. This is functional for
the most common bindings, http-redirect and http-post. The code should
allow all other bindings to be implemented later.
* Added lots of documentation where changes were made