RFR: Implement shared caching for rest requests

[Robin Westberg]

Hi all,

Please review this change that implements caching for rest GET requests, as supported by at least GitHub.

Best regards,
Robin

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Commits:
 - 4f961967: Implement shared caching for rest requests

Changes: https://git.openjdk.java.net/skara/pull/471/files
 Webrev: https://webrevs.openjdk.java.net/skara/471/webrev.00
  Stats: 220 lines in 10 files changed: 196 ins; 2 del; 22 mod
  Patch: https://git.openjdk.java.net/skara/pull/471.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/471/head:pull/471

PR: https://git.openjdk.java.net/skara/pull/471