Move agents code into their own directory in src

[maximilien]

Move all agents file in new directory: src/agents/ The rationale is to have all agent code there. Eventually we could do the same for other logical groups. But at least we could start with agents. Especially the case as there are many many agent frameworks and we'd want to have support to many.

CC: @akihikokuroda

[akihikokuroda]

There are agent files in /tests and /demos directories. So we move them into /src/agents and change all references in the python files to the directory. Is it correct?

[maximilien]

No. Just the code in src. We can do similar consolidation in tests and demos separately. Thx