[MAJOR] use the new auth framework for http stats

[MAJOR] use the new auth framework for http stats

Support the new syntax (http-request allow/deny/auth) in
http stats.

Now it is possible to use the same syntax is the same like in
the frontend/backend http-request access control:
 acl src_nagios src 192.168.66.66
 acl stats_auth_ok http_auth(L1)

 stats http-request allow if src_nagios
 stats http-request allow if stats_auth_ok
 stats http-request auth realm LB

The old syntax is still supported, but now it is emulated
via private acls and an aditional userlist.