OPENDJ-1666 PR-19 CREST-3.0.0 Migration

Design changes overview:
* Make the code compiling against CREST-3.0.0
* Implement rest2ldap servlet and Http connection handler as a CHF filter/handler chain
* Move all of the functionality out of the opendj-rest2ldap-servlet module and into the opendj-rest2ldap module, since it doesn't require Servlet - Servlet integration is provided by CHF.
* Create an Ldap Http Handler which is shared by both rest2ldap servlet and httpConnectionHandler
* Remove Rest2LdapContextFactory because the authn filter and handler can communicate directly via Context objects rather than using Servlet "attributes".
* Rename Context to RequestState

Detailed changes performed:
Files which has been mostly modified:
* org.opends.server.protocols.http.CollectClientsConnectionFilter
* org.forgerock.opendj.rest2ldap.LDAPCollectionResourceProvider
* org.forgerock.opendj.rest2ldap.ReferenceAttributeMapper

Other changes are mostly minor, they just ensure that code compile against CREST-3.0.0.