RFR: 2167: Unify search methods in IssueProject

[Erik Duveblad]

Hi all,

this patch unifies the various ways of searching that exist within `JiraProejct`. I also chose to expose the `search` method in the `IssueProject` since I will make use of it in later patches. This is the first patch of _many_ that will extract the JBS specific parts from `JiraProject` so that `JiraProject` will be about JIRA and JBS specific functionality will be moved elsewhere. This refactoring is needed to allow other parts of the Skara to use JBS functionality with only an `IssueProject` instance (without turning `JiraProject` into effectively `JbsProject`).

Thanks,
Erik

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Commit messages:
 - 2167

Changes: https://git.openjdk.org/skara/pull/1610/files
 Webrev: https://webrevs.openjdk.org/?repo=skara&pr=1610&range=00
  Issue: https://bugs.openjdk.org/browse/SKARA-2167
  Stats: 59 lines in 3 files changed: 20 ins; 24 del; 15 mod
  Patch: https://git.openjdk.org/skara/pull/1610.diff
  Fetch: git fetch https://git.openjdk.org/skara.git pull/1610/head:pull/1610

PR: https://git.openjdk.org/skara/pull/1610