security-proxy - bumping to a new version of spring-security

The new version (3.1.x) introduces some extra classes that are
ActiveDirectory specific. Even if in the end I had to copy the entire
ActiveDirectory class, I think the shift could be useful in the future.

Tested on Rennes Métropole infrastructure.
security-proxy - adding a specific auth provider

In case of Rennes-Métropole, when using the User-Agent + HTTP basic
auth, we need to use 2 different authentication sources:

- A bind is first made onto the Active Directory, to ensure that the
  user is legit and provided a correct username / password ;

- The roles are then being fetched from an OpenLDAP ;

To achieve the use of both sources, it has been necessary to rewrite a
filter, based on ActiveDirectory from the spring security 3.1.x,
accepting an extra constructor parameter which returns the actual roles
of the user, fetched from the OpenLDAP. Hence the newly introduced
package.
security-proxy - improving custom authentication filter

Adds the ability to try a bind onto the OpenLDAP in case of failure on
the Active Directory. This should address the bugs related to
server-to-server communications, and removing the whitelisting.

This code is supposed to be rennes-project specific.

TODO: there will still be some issues on sig-test instance

* SSL certificates mismatch while extractorapp -> geoserver
* there is still a whitelist when geofence -> geoserver, which
causes false positive result reguarding to the current code
modification.
Merge pull request #687 from pmauduit/security_proxy_mixing_authentication_sources

security-proxy - mixing LDAP authentication / roles mapping sources