RFR: Use a service provider to create issue trackers

[Robin Westberg]

Hi all,

Please review this refactoring that makes use of a service provider to create issue trackers, similarly to how forges are handled.

Best regards,
Robin

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Commits:
 - 1549c96f: Related whitespace cleanups
 - 20ee09d3: Use a service provider to create issue trackers

Changes: https://git.openjdk.java.net/skara/pull/229/files
 Webrev: https://webrevs.openjdk.java.net/skara/229/webrev.00
  Stats: 698 lines in 13 files changed: 382 ins; 307 del; 9 mod
  Patch: https://git.openjdk.java.net/skara/pull/229.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/229/head:pull/229

PR: https://git.openjdk.java.net/skara/pull/229