Confirmed Opt In page

At this moment per list 2 URL's are defined: an unsubscribe URL (UnsubscribePage) and a confirmation URL (ConfirmationSuccessPage). But when a list has the ConfirmedOptIn checkbox checked, it would be nice if an extra form field appeared to enter the URL of a page which says something like "Thank you for subscribing! We sent you a confirmation email, etc.".

I tried to add this extra URL (ConfirmedOptInPage):

1. includes/campaignmonitor_list.admin.inc: I added text fields to the Create list and Edit list forms, form states show / hide this field;
2. includes/campaignmonitor_list.admin.inc: The other 2 URL's (UnsubscribePage and ConfirmationSuccessPage) are stored at Campaign Monitor's servers, but this URL had to be stored in this list's options variable. The Create list form did not save any values in the list options variable yet, so I added this for this field. And the Edit list form removed all fields in the Options fieldset before saving, I manually added the new field's value to the lists' options variable;
3. campaignmonitor.module and module/campaignmonitor_user.module: I altered the argument of the goto() depending on whether ConfirmedOptIn is checked and ConfirmedOptInPage is defined;
4. lib/campaignmonitor.class.inc: createList() returned a true value on success, I changed this into the list id so the caller receives the list id. With this list id I could save ConfirmedOptInPage in the list's options variable on Create list form submit.

I hope this addition makes any sense and since I am fairly new to Git / diffs / patches, I also hope the attached diff is okay.

Cheers.