Cache KeyStore on start

[Zhaars]

Implementation of caching keystore keys on start of the AcraServer. Implementation based on ListKeys keystore method which was unimplemented for v1 keystore.

Checklist

• [x] Change is covered by automated tests
• [x] The coding guidelines are followed
• [x] Public API has proper documentation in the Acra documentation site or has PR on documentation repository with new changes
• [x] CHANGELOG.md is updated (in case of notable or breaking changes)
• [x] CHANGELOG_DEV.md is updated
• [x] Benchmark results are attached (if applicable)
• x are up-to-date (in case of API changes)