On power up, advertise aggressively for at least 30 seconds then switch
to a longer interval to conserve battery life. This fast/slow pattern
is designed to balance connection response time and battery life.
When a disconnect event is received restart the fast/slow pattern.
When a failed connect event is received, restart the fast/slow pattern.
When the screen is activated and ble is not connected, restart the fast/slow pattern.
This pattern is consistent with Apple's BLE developer standards (QA 1931).