Handle staging_continuation data and refactor out new_user_time couchdb view

Fixes #56, now gets kpi blobs from users at the time the blob was created, instead of the next go-round. Users who come back after closing the dialog while waiting for email verification have a "staging_continuation" event in the event stream, this PR handles that new event. Incidentally, refactors out the new_user_time couchdb view, as we can just reuse new_user. (new_user_success and its segmentation relatives can go as well, but that will be a future PR).