Fix delete client when deleting list item

There's a problem with the way nested Backbone views are implementing events:

* The "client registration" view listens for "click .btn-delete" in order to run `deleteClient`
* The list of contact emails view listens for "click .btn-delete" in order to run `deleteItem`

... but this means when a user deletes a contact, the entire client gets deleted, too (or at least, an alert pops up asking to confirm client deletion). Yikes!

This PR is a minimal fix. But the right solution would involve *not* matching all internal button-clicks from the client registration view. (I would have taken a stab at that, but then I saw the code duplication across `dynreg.js`, `client.js`, and `admin.js`, and couldn't understand what was going on.)

Also corrects a usability bug in the list controller, which lets you "leave text hanging" in the `redirect_uri`  or `contacts` inputs if you forget to click `+`.