Heated rear seats control (left and right, on/off) #34

Extend heated seat control to the rear seats. Today only front seats are supported (RvcReqType.HEATED_SEATS, params 17 and 18). The rear param IDs are unknown, and rear status fields are missing.

Part of #26. Needs a live capture of the iSmart app traffic from an MG S6 (to be done separately).