Indicate that brake sensors / shift sensor are being engaged

[rdancer]

There is no indicator of brake sensors/shifter sensors being engaged.

This would provide useful feedback, and also allow e-brake installation/adjustment/diagnostic while the bike is stationary.

The SW-900 e-bike display for example shows "Error 2" whenever brakes are depressed.

• Use the indicator area at the bottom of the 860C where "LIGHTS" is displayed when lights are on to show "BRAKES"
• In the technical section of the config menu, show an item that brakes are "on"/"off"
• For the headless controller, use an LED that comes on whenever brakes are engaged (not tested, may be already the case?)
• For SW102, show a small dot whenever brakes are engaged (not tested, may be already the case?)

Related issue is that the firmware freezes on the boot-up screen: https://github.com/rdancer/TSDZ2-Smart-EBike/issues/2

[rdancer]

This is implemented in the code, and it does actually show on my device

https://github.com/rdancer/Color_LCD/blob/f22fe053c1932a49dfabae52532464f0d0e400ac/firmware/common/src/mainscreen.c#L1078