Add truncate and pop to ProofListIndexProxy [ECR-3669]

[dmitry-timofeev]

Overview

Extract these operations to the interface. Move their tests
to the base test of interface operations, make some of them
parameterized.

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See: https://jira.bf.local/browse/ECR-3669

Definition of Done

• There are no TODOs left in the code
• Change is covered by automated tests
• The coding guidelines are followed
• Public API has Javadoc
• Method preconditions are checked and documented in the Javadoc of the method
• Changelog is updated if needed (in case of notable or breaking changes)
• The continuous integration build passes

[coveralls]

Coverage remained the same at 85.735% when pulling 5bbfa2d on dmitry-timofeev:truncate-pop-ECR-3669 into a5cc533 on exonum:master.

[MakarovS]

👍