Improving react to contact and potentially breaking plugin changes

Breaking

• on_thread_initiate and on_thread_ready events now have thread, creator, category, initial_message as additional arguments.

Fixed

• confirm_thread_creation now properly works when a user opens a thread using react to contact. (GH #2930, PR #2971)
• ?disable all/new now disables react to contact threads. (GH #2969, PR #2971)
• Ghost errors are no longer raised when threads are created using non-organic methods.

Internal

• thread.reply now returns (msg_to_user, msg_to_thread). Can be useful in plugins.