aaa: Using extensions API

This patch  uses the extensions API
(Internal/KerberosLdap) in a gradual manner
1. Changing LoginBaseCommand and AuthenticationFilter to work directly with the new API
2. Introducing AuthzUtils as helper class for authorization
3. Changing KerberosLdapDirectory to implement Extension, and base all the code
on search of principals and groups
4. Changing AuthenticationProfileRepository to work with Extension proxies
5. Changing extension manager

Change-Id: I916012eab61a96bdb0f366d9dc8462325d7f726f
Topic: AAA
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>