Add a cron job to poll an imap inbox for mail bounces

[Hugh Davenport]

Checks an imap mailbox, assumes that you have set up a
seperate mailbox for recieving the mailbounces.

To enable this change, the php imap extension must be loaded

This uses 9b9b2a5c25a078d0c6aab0e4fb6bed1c5eb112d2 for the
mail bounce checking. It also adds a few extra config.php
settings that need to be set for this cronjob to work.

The config settings that need to be set are:
$cfg->bounces_handle = true
$cfg->bouncedomain
$cfg->imapserver

There are also some other options shown in lib/config-defaults.php
for power users.

[Hugh Davenport (hugh-davenport)]

https://reviews.mahara.org/#/c/1181/

[Hugh Davenport (hugh-davenport)]

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