refactor(registry): s/GetLatestVersion/LatestVersion/
refactor(registry): s/GetAllJobs/Jobs/
refactor(registry): s/GetJob/Job/
refactor(registry): s/GetJobTarget/JobTarget/
refactor(registry): s/GetJobTargetState/JobTargetState/
refactor(registry): Drop GetSignatureSet from Registry iface
refactor(registry): s/JobSignatureSet/JobSignatureSet/
Merge pull request #561 from bcwaldon/registry-renaming

Simplify Registry methods