Add bluetooth device tracker (#1830)

This tracker discovers new devices on boot and tracks bluetooth devices
periodically based on interval_seconds value. Devices discovered are
stored with 'BT_' as the prefix for device mac.

Requires PyBluez

script/gen_requirements_all.py

@@ -10,6 +10,7 @@ COMMENT_REQUIREMENTS = [
     'RPi.GPIO',
     'Adafruit_Python_DHT',
     'fritzconnection',
+    'pybluez',
 ]