Add bluetooth threshold settings

[mattudakis]

The photoresistor on the clock uses a threshold to determine the brightness. This threshold will depend on the environment position that the clock is located.

For example: The photoresistor in a clock positioned near a window will read vastly different to that in a clock in a darker corner of a room.

Two possible solutions:

1. Use Bluetooth serial connection to be able to adjust this threshold remotely and save the value in the eprom memory
2. more elegant; the clock learns the max and min photoresitor levels over a 24hour period from being powered on and autoupdate the threshold to eprom.

will likely implement solution1

[mattudakis]

After testing this might not be needed. Will keep this open in case of future problems