refs #246

added the ldap_authenticatable to connect and bind a user in ldap server.
created the migrate files to update sites table and add ldaptoken table.

next commit will finish ldap_authenticatable and start the account create
process within ldap_controller.
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;
refs #246

Finished the LDAP authentication code.

Updated locale file (mconf.yml) to get error messages, and information for the
site page (set the LDAP variables).

Updated the login page to present a checkbox for LDAP authentication

Updated the Site page (from administrator -> Manage)

Waiting for the feedback from users for future changes.
First general review of the authentication via LDAP

- Reorganized the strings in the locales to use lazy lookup
- Moved the authentication class from config/initializers to lib/devise/strategies
- Moved the migrations to the bottom of the list
- Reviewed the authentication class to prevent a few errors and add more information
  in the log files
More log messages and less errors in the authentication via LDAP

The most important change was when creating a new user. The values passed need
to be ruby strings, but they were classes defined by net-ldap. This was causing
errors in the gem "valid_email", so now we make sure the values will always
be strings.
More details at: https://github.com/hallelujah/valid_email/issues/22

refs #246