To be able to pair properly using SSP the BT device have to know
which services we're running, thus we need to register SDP entries
after startup of the BT stack
This enables Simple Secure Pairing which is required to pair
from another device (device -> Pure). As for now, only KeyboardOnly
capabilities are enabled as we have all frontend and backend
already enabled for entering the pin code/passkey
Due to enabled EHCILL the shutdown procedure takes longer time
than before, so restarting by turning off and on without a delay
caused crash in the BT stack. Added delay between shutdown and
power on to let the stack turn off completely
Reworked AppSettings handling of BT devices to be prepared for
handling the HFP profile, eliminating by the way few bugs and
speeding up the flow (by getting rid of few refreshes).
Added unit tests for handling the BT devices flow
