Added bulkclose feature to the githubPRs script

[janhoy]

Example use:

./githubPRs.py \
  --bulkclose "Lucene and Solr development has moved to separate git repositories and this PR is being bulk-closed. Please open a new PR against https://github.com/apache/solr or https://github.com/apache/lucene if your contribution is still relevant to the project." \
  --token XXXXXXXXXXXXX

Result of such an action can be seen in #1364 which I used for testing. You can then easily query GitHub for a list of the stale-closed PRs: https://github.com/apache/lucene-solr/pulls?q=label%3Astale-closed+is%3Aclosed

[rmuir]

-1 to adding bulk close functionality

[rmuir]

That's an actual veto. justification: read the fucking mailing list thread, see how @janhoy tried to "slip this in" under the pretense of a +1. Several of us are against bulk-closing on the thread. It is more people, than are for it. Consensus is not with you. Passive-aggressive shit like this doesn't help.