RFR: issuetracker: add Label class [v2]

[Erik Helin]

> Hi all,
> 
> please review this patch that introduces the `Label` class in the `issuetracker` package. The `Label` class provides access to an eventual description of the label, previously we only returned the label names. The majority of the patch is a simple refactoring of changing existing calls to `Issue.labels` to `Issue.labelNames`.
> 
> Thanks,
> Erik

Erik Helin has updated the pull request incrementally with one additional commit since the last revision:

  HostedRepository.labels

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Changes:
  - all: https://git.openjdk.java.net/skara/pull/1089/files
  - new: https://git.openjdk.java.net/skara/pull/1089/files/0d2b4bbd..1b444b29

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=skara&pr=1089&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=skara&pr=1089&range=00-01

  Stats: 26 lines in 5 files changed: 25 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/skara/pull/1089.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/1089/head:pull/1089

PR: https://git.openjdk.java.net/skara/pull/1089