Use protobuf-java-util for protobuf parsing (to and from JSON)

[tomasulo]

Description of the Change

I propose to use http://mvnrepository.com/artifact/com.google.protobuf/protobuf-java-util for parsing protobuf messages to and from JSON instead of a combination of self-written code and http://mvnrepository.com/artifact/com.googlecode.protobuf-java-format/protobuf-java-format.

Benefits

• Exchanging protobuf-java-format (is not being maintained anymore, last release: November 2015) with the actively maintained protobuf-java-util
• protobuf-java-util provides standardized serialization and deserialization
• version of protobuf-java-util matches the protobuf version we use in the projects
• using official code published by google instead of our own version

Possible Drawbacks

None, as far as I know.

[bkrahmer]

Thomas, I think the implementation looks great. I think we need some more test cases before I'd be comfortable merging it, however. enums, byte strings and sub-messages are my main concerns.

[tomasulo]

Okay, I will add some more testcases.