Implement JSON-RPC notifications

[fdechelle]

• detection event
• other events

[fdechelle]

• add event source in scan
• in "scan" method add listener to event source
• in listener send notifications

[fdechelle]

• move various counters in ondemand.c
• add progress_event firing in ondemand.c
• fix detection event problem:
  • A: add context (like scan_id)
  • B: add listener on the right source (i.e. a6o_on_demand)