Shorter serializations of Representations

[JanBobolz]

Added new BinaryFormatConverter that serializes Representations to byte[] and back.
This format is much more compact format than JSONConverter's.

The efficiency gains are mostly because:

• No Base64 encoding of ByteArrayRepresentation (and BigIntegerRepresentation) is needed - each such value just ends up "as is" (in two's complement) in the binary format.
• If some String (or class name) is referenced multiple times, it is only encoded once, all occurrences are replaced with a 4-byte reference to the String.
• The caller can optionally pass a list of "well-known" strings and class names, in which case these Strings don't end up in the serialization format at all (again replaced by a short reference). So Strings like "de.upb.crypto.math.structures.zn.Zn" don't have to appear in the serialization format at all if the caller provides those ahead of time.