CR-5463 OPENIG-325 Cannot use exchange.request.uri as lvalue-expression
The issue was due to the BeanELResolver involded by the use of Expression
which was unable to get the right setter to set the URI.
Solution was to create a RequestResolver, to guide it through the setters to get
the right one and to finally be able to write the uri as expected.

- added RequestResolver.class
- added unit tests for the new RequestResolver class.
- added unit tests for the AssignmentFilter about URI change.

Thanks to Guillaume for his help.

git-svn-id: https://svn.forgerock.org/openig/trunk@754 dbb9e58e-28e6-4ce0-90e8-f11d9605b710
OPENIG-384 Merge FederationServlet into SamlFederationHandler (no other changes)

git-svn-id: https://svn.forgerock.org/openig/trunk@755 dbb9e58e-28e6-4ce0-90e8-f11d9605b710
OPENIG-384 Use OpenIG session, request and response instead of servlet's objects

Reserve real usage of HttpServletRequest and HttpServletResponse objects for
Fedlet classes only.

Session attributes' variables `subjectMapping`, `sessionIndexMapping`,
`authnContext` and all of the `attributeMapping` values are now stored in
the OpenIG Session object (instead of the `HttpSession`). That makes it possible
to use theses values inside OpenIG configuration files (through `Expression`).

git-svn-id: https://svn.forgerock.org/openig/trunk@756 dbb9e58e-28e6-4ce0-90e8-f11d9605b710