re-implement interactions and canvas to better support concurent generations

Massive work, the gist is, the canvas/interaction infrastructure was never meant to support concurrent generations, race/workflow/ whatever madness.

it needs a complete overhaul to be able to have :
* multiple conversation "tabs" seen that in one of the Hackaton entry, it is brilliant !
* streaming race/workflow step content
* multiple tabs streaming at once

on mounting a tab/interaction tab should subscribe to the content stream, unsub on unmount !
canvas should not be responsible for push the streaming data