new silence mode, voltage threshold are floats, new default for "Telemetry Check Interval"

- Silence Mode: 2-pos switch in Down-Position during power on
Transmitter turns off buzzer and uses LED instead.
- config.h accepts now directly float values for voltage thresholds
g_Profile[].V_A1[], g_Profile[].V_A2[] and g_V_TX (no calculation
needed)
- default for g_Telemetry_Check_Interval is 8000ms