user preferences and chat properties are all stored in index.ttl

[bourgeoa]

user preferences and chat properties are all stored in index.ttl
This imply Write for chat owner and users.

As a consequence :

• every allowed user can edit/delete index.ttl
• chat owner cannot manage the chat parameters to is liking

[bourgeoa]

proposal

• index.ttl should be Read for users and Write for chat owners
• store user preferences in participation.ttl with users Write