refs #246

Finished first version of function - ldap authentication -

DONE:
The ldap_authenticatable.rb file binds to the ldap server, binds the
user and creates the user account (if it does not exist) or associate
an account with the same email to the ldap account.

TO DO:

update the view to set site variables for ldap;

update the view to log in (add a ldap button choice);

create tests routines to ldap functions;