Upgrade ntlm_fake_auth helper and internal libntlmauth

Upgrade ntlm_fake_auth helper and internal libntlmauth

Fake auth helper changes:

 - renames fakeauth to ntlm_fake_auth
 - links ntlm_fake_auth to libntlmauth
 - removes duplicate code provided by libcompat and libntlmauth
 - moves the remaining bits of fakeauth/ntlm.h to ntlm_fake_auth.cc

Library API changes:

 - moves some of the basic NTLM operations into libntlmauth
    * fetch_string UNICODE support
    * make challenge packet
    * validate packet type
    * make challenge nonce
    * unpack user and domain from authenticate packet

 - tweaks libntlmauth to split the make challenge operation so that it
   only generates the challenge object (does not encode blob for sending,
   or hard-code field values any more).

Other related changes:

 - tweaks the smb_lm helper which already linked libntlmauth so that it
   uses the updated API correctly after the above changes.

 - documents libntlmauth and some of ntlm_fake_auth helper