Support XKMS 2.0

Talend is happy to donate the initial XKMS 2.0 implementation to Apache CXF as part of this Jira.

XKMS will be contributed as a service (like STS and WS-Discovery) providing standardized access to central public key infrastructure (PKI) including lookup, validation, registration, reissuing and revocation of public keys.
XKMS will help users to manage their certificates centrally instead storing them into local keystores, that IMO best practice for middle/large service landscapes.

I tried to describe the use case, architecture and design of XKMS Service in CXF wiki:
https://cwiki.apache.org/confluence/display/CXF20DOC/XML+Key+Management+Service+%28XKMS%29
and in the blog: http://ashakirin.blogspot.de/2013/04/cxf-security-getting-certificates-from.html .

Attached is the initial draft of XKMS service implementation supporting X509 public keys, simple File and LDAP storages and providing Web and OSGi deployment. Suggested target CXF release for XKMS service will be 3.0. Code was designed and implemented by me together with Christian Schneider (cschneider), reviewed and refactored by Jan Bernhard (jbernhard) and donated by Talend company.

Any feedback for this code is welcome. The next tasks will be support revocation lists, complete validate operation for trusted chains, extend system tests, support new key storages.

Regards,
Andrei.