added multimode, 7analog mode
RX mode should be decided during flashing for safety purposes but TX will be able to talk to any RX by changing the "mode" from lua Script to match the RX.
TX default switch mode is as what was selected in user_defines.txt.
in 7 analog mode, CH4 (AUX1) is still arming switch but CH5(AUX2), CH6(AUX3), CH7(AUX4) is analog and 8 bits only and not CRC checked, as analog7 mode main purpose was to add 3 extra analog channel for headtracker.