RFR: 2164: Add git notes notifier [v3]

[Erik Duveblad]

> Hi all,
> 
> please review this patch that adds a new notifier that records the link to a commit, the link to the review and ev. links to issues in a [git note](https://git-scm.com/docs/git-notes). This will make it possible to view this information using e.g. `git log` or `git show` _without_ having these URLs in the commit message itself. Git notes are also modifiable (they are just blobs referred to by a ref), so they can be updated if ever change the scheme or domain for these links.
> 
> I also added two unit tests for testing the new notifier.
> 
> Thanks,
> Erik

Erik Duveblad has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Merge branch 'master' into note-notifier
 - Add configuration test
 - Merge branch 'master' into note-notifier
 - 2164

-------------

Changes:
  - all: https://git.openjdk.org/skara/pull/1608/files
  - new: https://git.openjdk.org/skara/pull/1608/files/3cbff60f..495efc2b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=skara&pr=1608&range=02
 - incr: https://webrevs.openjdk.org/?repo=skara&pr=1608&range=01-02

  Stats: 161 lines in 40 files changed: 73 ins; 3 del; 85 mod
  Patch: https://git.openjdk.org/skara/pull/1608.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1608/head:pull/1608

PR: https://git.openjdk.org/skara/pull/1608