We only have the means to generate a transient NameID. If a different
one was requested, the code would crash because nameIdValue would
be unset. Fix that we fall back to transient in such a case.

No functional changes

Partially reverts b7c2caad
and fc1ffee7

Closes: #1660

This reverts commit 8bd8e3f4.

This reverts commit cd4cb9d4.

Closes:  #1659

Make sure the `saml:IDPList` and `IDPList` parameters are not overloaded. From now on, saml:IDPList is being used when SSP is used as a proxy while the IDPList parameter is used when SSP is used as in SP-mode and you want to apply scoping to your AuthnRequest.

See https://github.com/simplesamlphp/simplesamlphp/pull/1563 for the full explanation of the changes.

Add some controllers + tests