[IM|HK] Move traffic stats to database CLI tool to a better home
[NF] CLI tool to email a report on ports with error / discard counts

This commit introduces two new CLI actions:

    ixptool.php -a statistics-cli.email-ports-with-errors
    ixptool.php -a statistics-cli.email-ports-with-discards

Which emails a report (including graphs) of any member ports have error
or discard counts from 'yesterday'.

A new configuration block is required:

    ; note that the %s in the subject below is replaced
    ; with Errors / Discards as appropriate by the script
    ;
    cli.ports_with_counts.from_email = "ops@example.com"
    cli.ports_with_counts.from_name  = "IXP Operations"
    cli.ports_with_counts.subject = "IXP - Ports with %s"
    cli.ports_with_counts.recipients[] = "someone@example.com"
    cli.ports_with_counts.recipients[] = "someone-else@example.com"

The documentation has also been updated:

https://github.com/inex/IXP-Manager/wiki/Email-Notifications