logging: Added BLE Backend Service

Added a new logger backend to recieve data over a BLE
notification characteristic.
The characteristic is based on the UUID from the Nordic connect SDK
service NUS, which allows to have a UART shell over BLE.
The idea behind this, is that this logger can be used directly
with the NRF apps or any other BLE UART terminal app.

Signed-off-by: Victor Chavez <chavez-bermudez@fh-aachen.de>