Add protobuf-backed proof support: [ECR-3666] (#1293)

Add a MapProof and a ListProof that are wrappers around
the corresponding protobuf messages.
The wrappers will allow us to extend the set of operations
post 1.0.

Make all proof constructors in ProofMap and ProofList
return the new classes (#getProof etc.).

Separate integration tests for proof creation (getProofX)
and verification (verifyProofX).

Remove no-longer used by native fromNative.

Remove obsolete classes supporting tree-like list proof representation.

Author: dmitry-timofeev

exonum-java-binding/CHANGELOG.md

@@ -15,6 +15,17 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+- Support of creation of Protobuf-based proofs for maps and lists.
+  Such proofs can be easily serialized using Protocol Buffers
+  and sent to the light clients.
+  See `ProofMapIndexProxy#getProof` and `MapProof`;
+  `ProofListIndexProxy.getProof`, `ProofListIndexProxy.getRangeProof` and
+  `ListProof`.
+  
+### Removed
+- Classes supporting no longer used tree-like list proof representation.
+
 ## 0.9.0-rc2 - 2019-12-17
 
 ### Fixed