Include username and email in downloaded analytics

Created by: mike-r-mclaughlin

Requested by: https://github.com/sourcegraph/accounts/issues/3

Feature request description

Currently when downloading analytics from site-admin/usage-statistics, there is a column for user_id. This appears to be the Sourcegraph user ID. It would be better if this included the username and/or the email address.

Is your feature request related to a problem? If so, please describe.

When providing this data to another non-site administrator, it's hard to match up the user id to the actual user.