Rename Bluetooth stack function parameters to clearly indicate what sort of Bluetooth...

Rename Bluetooth stack function parameters to clearly indicate what sort of Bluetooth channel (ACL, RFCOMM) is required for each parameter, to make the code easier to read.

Add a new RFCOMM_ChannelSignalsReceived() Bluetooth stack callback from the RFCOMM layer for when the remote device sends new terminal control signals.

Fix RFCOMM_SendData() not aborting correctly when the requested RFCOMM channel is not found.