RFR: notify: prefix event handlers with "on*"

[Erik Helin]

Hi all,

please review this refactoring that prefix the event handles in the notify bot with `on` instead of `handle` (I also
renamed some handlers for consistency).

Testing:
- [x] `make test` passes on Linux x64

Thanks,
Erik

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Commit messages:
 - notify: prefix event handlers with "on*"

Changes: https://git.openjdk.java.net/skara/pull/653/files
 Webrev: https://webrevs.openjdk.java.net/skara/653/webrev.00
  Stats: 35 lines in 9 files changed: 0 ins; 0 del; 35 mod
  Patch: https://git.openjdk.java.net/skara/pull/653.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/653/head:pull/653

PR: https://git.openjdk.java.net/skara/pull/653