Refactor messaging layer.

[marcofavorito]

Proposed changes

This PR restructure the messaging layer of the software.

Fixes

None.

Types of changes

What types of changes does your code introduce to agents-tac? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• [x] I have read the CONTRIBUTING doc
• [x] I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• [x] Lint and unit tests pass locally with my changes
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have added necessary documentation (if appropriate)
• [x] Any dependent changes have been merged and published in downstream modules

Further comments

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[DavidMinarsch]

LGTM