Rename BadgeInstance context specifier, add option to get instances by user email

This renames the BadgeInstance context specifier from "email" to "instance", which is vastly more reasonable The old "email" specifier remains valid.  I didn't add any logging when the old specifier is used, but can do so if that is desired.

This also adds an optional "email" argument to getBadgeInstances.  When used, it will list badge instances within the specified context that were awarded to the email address provided.