RFR: git-pr: add "URL" column to "git pr list"

[Erik Helin]

Hi all,

please review this small patch that adds a URL column to `git pr list`.

Testing:
- Manual testing of `git pr list`

Thanks,
Erik

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Commits:
 - 51dd886a: git-pr: add "URL" column to "git pr list"

Changes: https://git.openjdk.java.net/skara/pull/479/files
 Webrev: https://webrevs.openjdk.java.net/skara/479/webrev.00
  Stats: 5 lines in 1 file changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/skara/pull/479.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/479/head:pull/479

PR: https://git.openjdk.java.net/skara/pull/479