Management command to email users

[clbarnes]

Could be filtered by login date, whether they're active, etc. Would be useful for planned maintenance.

[clbarnes]

Simple half-solution (as emailing directly from the instance may or may not be possible based on configuration) is a management command to list (and filter) users, including their email addresses, in a form which can easily be awk'd to get the email addresses. This would also require a couple of minor changes to keep stdout clean for the output:

• redirecting stdout to stderr while the R environment is fired up, because by default it dumps version info etc. to stdout
• setting the management command log handler to write to stderr rather than stdout