Fix JIRA integration from "arc" commit messages

Summary: Fixes T4683. This was just a missing method implementation. Also provide a couple of translation things.

Test Plan:
  - Created a revision from the command line with a nonempty `JIRA Issues:` line, via `arc diff`.
  - Looked at the translation strings.

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley

Maniphest Tasks: T4683

Differential Revision: https://secure.phabricator.com/D8656