FYI: notify: rename JsonUpdater to JsonNotifier

[Erik Helin]

Hi all,

please review this small refactoring that renames `JsonUpdater` to `JsonNotifier`.

Testing:
- `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - notify: rename JsonUpdater to JsonNotifier

Changes: https://git.openjdk.java.net/skara/pull/647/files
 Webrev: https://webrevs.openjdk.java.net/skara/647/webrev.00
  Stats: 810 lines in 10 files changed: 401 ins; 408 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/647.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/647/head:pull/647

PR: https://git.openjdk.java.net/skara/pull/647