Proposal aggregate

[vil1]

Specify and implement commands/events/projections attached to the Proposal aggregate.

See the wiki for the related events

The Proposal aggregate is responsible for managing :

• votes of the committee
• communication between the speaker and the committee

A Proposal can be attached to at least one Speaker.

Specific documentation of the Proposal aggregate must be added to the corresponding wiki page

As mentioned in #7 it might be worthy to merge this aggregate with the Draft aggregate