Add protocol version 7 and genesis data

[limemloh]

Purpose

Add protocol version 7 boilerplate, at this point it should behave the same as P6.

Part of Concordium/concordium-node#1066.
Should be merged after Concordium/concordium-grpc-api#49.
See also Concordium/concordium-node#1075.

Checklist

• My code follows the style of this project.
• The code compiles without warnings.
• I have performed a self-review of the changes.
• I have documented my code, in particular the intent of the
  hard-to-understand areas.
• (If necessary) I have updated the CHANGELOG.