Feature/saml replaying

Everything done for: https://github.com/OpenConext/OpenConext/issues/1
- [x] Moved functional testing and mock SP / IdP to separate repo.
- [x] Added some more metadata to composer.json
- [x] Allow injection of ID, Time and superglobals (but only in functional-testing environment)
- [x] Add JANUS Fixture client and allow injection of JANUS data via the fixture.
- [x] Fixed bugs in Response generation.