[Engine-Twitter] Delay the Connected event launch a bit more

Let's get the events be fired at the end of Connect(), rather than
at the middle.
[Engine] Execute the OnConnect Commands in a thread

They could take some time so it is better to launch them with the
threadpool.
[Engine-Twitter] Delay the UI usage in the timeline command

The timeland command should launch the new chat only when it has
retrieved all data needed for the chat.