Improve LDAP authentication * Adds an LDAP filter for locating the LDAP object * Adds a search scope policy when using the Base DN * Adds option required certificate policy when using LDAPS * Adds attribute mapping for username, firstname, lastname, email * Initializes rhodecode user using LDAP info (no longer uses "@ldap") * Remembers the user object (DN) in the user table * Updates admin interfaces * Authenticates against actual user objects in LDAP * Possibly other things. Really, this should be extended to a list of LDAP configurations, but this is a good start.