Split functionality of binding message and context

[Torsten Lodderstedt]

• provides verifiable binding between consumption and authentication device
• usually generated by the OP, mandatory to be provided by the RP in the server-initiated case (see below)
• need to have additional parameter (context) to provide RPs option to describe context and purpose of the transaction in free text

[Axel Nennker]

This issue is dormant now for nearly a year... I think we should put this issue either "onhold" or "close" is. We can always reopen or recreate if we find a use case where binding_message is not enough and user questioning too much.

[Jörg Connotte]

I think we already decided to address the context topic separately.