RFR: 73: Improve email threading, add separate approval email

[Robin Westberg via github.com]

Hi all,

Please review this update to the mailing list bridge bot, that improves threading of messages and also adds a separate approval message.

Best regards,
Robin

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Commits:
 - ef0be99b:	Improve email threading, add separate approval email

Pull request:
https://git.openjdk.java.net/skara/pull/121

Webrev:
https://webrevs.openjdk.java.net/skara/121/webrev.00

Patch:
https://git.openjdk.java.net/skara/pull/121.diff

Fetch command:
git fetch https://git.openjdk.java.net/skara pull/121/head:pull/121