Merge branch 'uwmadison-attr' into 'master'

Add UDDS attribute and refactor

Apologies for the large and hard to read PR--it should hopefully make the code more easy to read and navigate.

This PR adds UDDS as an attribute for `UserDetails`, along with a new class, `PreauthUserDetailsProvider`, which is an implementation of `UserDetailsProvider` for UW-Madison login.

Notable changes:
1. 'HTTP' is now assumed by default. This is the flag that can be passed to `Preauth` constructors for the 'HTTP' versions of attributes. Example: `wiscEduPVI` becomes `HTTP_WISCEDUPVI`.
2. `UserDetailsProvider` is an abstract class now, not an interface.
3. Constants used for header keys are much more consistent. Keys for UW-System login no longer have the `FED_` prefix and you will get the correct key for your particular implementation (`FederatedPreauth...` vs. `Preauth`) by using `static::<CONSTANT_NAME>`. *The only exception:* UWMSN and UW-System differ on their name for 'PVI'--UWMSN uses "PVI" and UW-System uses "SPVI", so `PVI` is only a constant in `PreauthUserDetailsProvider` while `FederatedPreauthUserDetailsProvider` has an `SPVI` constant.
4. *Namespace reorganization*. Rather than lumping everything into the `edu\wisc\doit` namespace, the namespace structure is now much  more like [uw-spring-security](https://git.doit.wisc.edu/adi-ia/uw-spring-security). General classes now exist in the `edu\wisc\doit\uwphps` namespace, with `local` and `preauth` namespaces existing for the local and preauth implementations. This change necessitated the bump to 2.0.0.

Please review: @ahoffmann @weizhong-wang @KJOYNER

See merge request !8