Added function to get elapsed time since start in msecs in DCPServer.
Added function getCentralSessionForStation in DCPServerCentral.
Added send setSessId to drone when command station request connection.
Added getStation to DCPServerCentral.
Added send disconnect to other communication end (command or drone) when receiving disconnect request from remote (command or drone).
Added send disconnect to other end (command or drone) if remote says bye without previous disconnect.
Added log for disconnect and setSessId.