/notify/claim responds more quickly, and supports bulk issuing

/notify/claim's behavior changes as follows:
- It will now send a response without waiting for a response from mandrill, if it sends an email.  This is probably better behavior in the first place, and will support faster issuing when lots of badges are issued at once.
- You can now send it an array of claimCode/email pairs instead of a single claimCode and email, if desired.  Nothing uses this functionality yet, but it might be used by openbadger to speed up issuing in the future.