Feature - REST API search now returns total count of filtered objects trough X-Total-Count response header

[Z14tk0]

Hi,

Note:
This is continuation of work from this PR #29 so if you decide to accept this PR we can close other one as this PR contains all that's needed.
For this to be validated you will need this MidPoint branch Evolveum/midpoint#232 (currently in PR).

Usage example:

        SearchResult<UserType> searchResult = service.users().search().queryFor(UserType.class).build()
                .options()
                .returnTotalCount()
                .get();

        searchResult.getHeaders().get(""X-Total-Count"")  //Should contain total count of filtered users

Let me know if you need me to do any additional changes or work.

Thank you, Best regards