RFR: 338: Send email notification for closed pull request

[Robin Westberg]

Hi all,

Please review this change that sends an email notification to review threads when the corresponding PR is closed
without being integrated.

Best regards,
Robin

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Commit messages:
 - Initial implementation

Changes: https://git.openjdk.java.net/skara/pull/565/files
 Webrev: https://webrevs.openjdk.java.net/skara/565/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-338
  Stats: 102 lines in 4 files changed: 102 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/skara/pull/565.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/565/head:pull/565

PR: https://git.openjdk.java.net/skara/pull/565