MetacatUI

This required some changes both in the d1_portal_servlet and MetacatUI.

I changed the portal servlet so that it handles errors better - e.g. when a username, organization, or password is missing OR when authentication fails. Now, when an error is caught, the portal servlet will redirect back to the given target with an 'error' URL parameter ('error=Unable%20to%20authenticate%20LDAP%20user') rather than throw a server error. So now the MetacatUI flow looks like this:

- User enters the wrong credentials and submits the login form
- LDAP auth fails in the d1 portal
- User is redirected back to the login form in MetacatUI with an error message