Allow arbitrary message sending

[d-roak]

Scenarios where we might want to have arbitrary messages:

• Node wants to broadcast a message to the pubsub (CRO) group which is not related to the CRO
  • In which case does this is true?
  • Should we allow apps to create custom pubsub groups for the case, a node needs awareness of other peers information that is not a CRO at all?
• Node wants to send a custom message to another node. We need to facilitate:
  • custom messages creation
  • custom handlers for those messages