Bug 1075692 - Fixing bug with single badge issuing

I broke single (non bulk) badge issuing from the badge page itself with my recent addition of bulk issuing.  Oops.

This fixes that.
I opted to allow for both "email" and "emails" in the request, as opposed to simply detecting when "emails" is an array of length 1.  This is because the behavior of badgekit-api is slightly different when bulk issuing vs. single issuing.  Most notably, it does not throw errors when bulk issuing if some of the email addresses already have the badge in question (it simply doesn't return that email address in the list of created badge instances).