[core] Fix SAML2 and commit upstream

Our SAML2 support is pretty buggy:

• csrf error when logging in
• unable to specify which NameID to use when logging in
• unable to sign authn and logout requests

so this issue is to track the fixes I'm working through with the upstream libraries. I've created forks of pysaml2 and djangosaml2 here:

• https://github.com/erickt/pysaml2
• https://github.com/erickt/djangosaml2

Both have branches named hue that when combined with hue should fix all the known issues when my hue patches land and these upstream pull requests are accepted:

• pysaml2: https://github.com/rohe/pysaml2/pull/164
• https://bitbucket.org/lgs/djangosaml2/pull-request/18/upgrade-pysaml2-to-210