RFR: 689: Do not automatically adjust labels after users intervenes

[Erik Helin]

Hi all,

please review this patch that disables the automatic labeling once the pull request author has issued any `/label`
commands.

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

Thanks,
Erik

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

Commit messages:
 - 689

Changes: https://git.openjdk.java.net/skara/pull/826/files
 Webrev: https://webrevs.openjdk.java.net/?repo=skara&pr=826&range=00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-689
  Stats: 33 lines in 2 files changed: 11 ins; 16 del; 6 mod
  Patch: https://git.openjdk.java.net/skara/pull/826.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/826/head:pull/826

PR: https://git.openjdk.java.net/skara/pull/826