base64 usage in payload values

[sake]

The payload fields in the envelope types mention in the description of the payload type that the type is "Base64 encoded json payload". This is also reflected in the examples in the message type. However there is no formal specification in the schema which makes the defined schema incompatible with the examples.

This leads to the situation, that

1. the schema can not be used to generate an implementation and to validate the correctness of the messages, or
2. the examples suggest to implement a variant which is not according to the specification.

To be honest I don't see any reason to encode the payload objects as base64. It furthermore complicates the parsing process unnecessarily.