160 ldap authentication

Threw away DB password-field authentication entirely, in factor of LDAP.

Use of LDAP is minimal (inspired by previous work with TAPER). It's used _only_ for authentication. All other user information (including staff first / last names) remains in the DB.

The only DB change made is dropping user.password. These code changes will work without that change (the column simply won't be used).

Some new info has to be added to cider_local.conf, as directed by the comments added to cider.conf. For example, these lines will make it work with Tufts' LDAP:

 ```
<authentication>
    <realms>
        <ldap>
	        <store>
           		ldap_server         ldap.tufts.edu
        		user_basedn         ou=People,dc=tufts,dc=edu           		
            </store>
    	</ldap>
    </realms>
</authentication>
```