Rename DBG_EMAIL option and Add it to debug_sample.php

We have nice feature, that allows to transfer all e-mails that are sent to given e-mail address.

This is useful in cases, when developer performs some action on a website, that can cause mass mailing and he doesn't want that mails to reach live users.

And since all e-mails are sent to his mailbox he then is able to detect what was happening.

Option is called DBG_EMAIL and can be set to:

e-mail address (e.g. al...@intechnic.com)
e-mail domain (e.g. @intechnic.com)

In later case actual recipient e-mail would be created from original e-mail recipient this way:

1. have user@domain.tld
2. replace @ with at
3. append domain from DBG_EMAIL
4. result user_at_d...@intechnic.com

If DBG_EMAIL is defined in $dbg_options array in debug.php file, then it will only work when debug mode is enabled. If there is a need, then it can be defined before $dbg_options array resulting recipient replacing until this option is turn off.

[B]In this task we NEED:[/B]

1. Rename DBG_EMAIL to OVERRIDE_EMAIL_RECIPIENTS
2. Make sure it works withi $dbg_options and outside
3. Add it as sample OVERRIDE_EMAIL_RECIPIENTS to tools/debug_sample.php

define('OVERRIDE_EMAIL_RECIPIENTS', ''); // Overwrites email recipients with some-email@domain-name.com or @domain-name.com