[cppmyth] TcpSocket more safe

Checking validity
[cppmyth] Starting thread event handler disconnected

Allow to start thread disconnected
[cppmyth] Returns thread status on event handler startup
[cppmyth] New event status "NOTCONNECTED"

Event handler announces EVENTHANDLER_NOTCONNECTED while not connected.
It informs client to do some action like sending wol packet magic etc...