doc: Created a new User Management doc to replace authentication.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Put architectural details of authentication in to architecture doc.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Restructured auth configuration reference.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Removed auth intro and auth docs and added user management to index.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Removed cephx guide. Replaced by user management.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Removed cephx intro. Moved details to user management, config, and architecture.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added user management link to quick start.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added a few comments and links to other relevant docs.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Minor changes.

Removed arch-related comments.
Added links to relevant docs.
Moved limitations to user management.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Added links. Clarified namespace comments. Added limitations.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Updated Keyring settings from comments and ceph-deploy defaults.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
doc: Provided additional detail on daemon-specific caps syntax.

Signed-off-by: John Wilkins <john.wilkins@inktank.com>
Merge pull request #2322 from ceph/wip-doc-authentication

doc: Refactored authentication docs.

Reviewed-by: John Wilkins <john.wilkins@inktank.com>