RFR: notify: use "listener" instead of "consumer"/"updater" in names

[Robin Westberg]

On Wed, 10 Jun 2020 13:59:34 GMT, Erik Helin <ehelin at openjdk.org> wrote:

> Hi all,
> 
> please review this refactoring of the notifier bot that uses the terminology "listener" instead of
> "consumer"/"updater". I also refactored how listeners are added to the `NotifierBot` (which now implements the
> `Emitter` interface).  Testing:
> - [x] `make test` on Linux x64
> 
> Thanks,
> Erik

Looks great!

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Marked as reviewed by rwestberg (Reviewer).

PR: https://git.openjdk.java.net/skara/pull/651