eCAL 6 Serialization / Msg API Review

[KerstinKeller]

The Message support (protobuf, capnproto, ...) are based on top of eCAL C++ API. We need to review this API carefully for the 6.0 release

eCAL Msg API

msg/publisher.h / msg/subscriber.h @KerstinKeller

• Subscribers are still using old school callbacks. Provide new callbacks
• Provide CMessagePublisher similar to CMessageSubscriber to add Serialization specific specific types a lot easier.
• Consider error Handler for Msg Subscribers in case of serialization errors.
  (Currently, with a subscriber, the user gets no feedback if the serialization fails. No callbacks are called, and he might just think that no new data is arriving).

canproto

• Review Publisher API, so that Send takes a builder instead of no arguments. (see also Using eCAL with capnproto #1843)

protobuf

• Server API based on v6 [core] protobuf service server to v6 #1964
• Client API based on v6 [core] protobuf service client to v6 #1981