Don't allow library registration to proceed unless all three required email addresses are present and user agrees to clickthrough.

[leonardr]

Registration with the library registry requires that the library have three email addresses set (see #912) and that the administrator agree to the library registry's terms of service.

The simplest time to verify that all these things are true is when the user clicks the "Register" or "Update registration" button, before the registration request goes out.

The most convenient way of doing this is to open a pop-up window that displays the text of the terms of service (with a "I agree" checkbox) and edit boxes for the three email addresses, similar to the text boxes found in the library configuration page. Once everything in the pop-up has been filled, any changes to the email addresses can be written to the database and a registration request can actually be sent out to the library registry.

Ideally, the terms of service would be obtained from the library registry itself, rather than hard-coded in the circulation manager, so that different registries could provide different language.