Add metadata to on_message callback

[herr-seppia]

Describe what you want implemented
The on_message callback must receive metadata related to the message received:

• Actual: on_message: fn(Vec<u8>)
• Needed: on_message: fn(Vec<u8>, MessageInfo)

MessageInfo should contain info about the actual kadcast broadcast height and the source peer address

Describe "Why" this is needed
The source address is needed as prerequisite to enable direct communication between nodes
The kadcast broadcast height is required to handle the manual propagation

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
"Manual propagation" is issued in #57
"Direct communication" is issued in #58