fixes #5222 - Log ldap attributes in debug-level logging
(cherry picked from commit d11f7309ef6f67699a750418f0f50afc589ff841)
fixes #4643 - Retrieving Optional LDAP attributes fails on 1.8.7
fixes #3827 - adds ldap avatar support
fixes #4442 - returning nil plays nice with try_to_login.
fixes #3312 - support /users/extlogin as a login page based on REMOTE_USER
fixes #2741 - rails 3 syntax
fixes #863 - added ldap_filter to LDAP auth sources to filter lookups using RFC 2254 filters
fixes #2411 - move STI models in /models and /lib/foreman/models to sub-folders