Migrated/refactored switchbot.bluetooth integration.

- Out `gattlib` + `pybluez`, in `bleak`. It's not platform-dependent, it doesn't
  require libboost and other heavy build dependencies, and it doesn't require the
  user that runs the service from having special privileges to access raw
  Bluetooth sockets.

- Better integration with Platypush native entities. The devices are now mapped
  to write-only `EnumSwitch` entities, and the status returns the serialized
  representation of those entities instead of the previous intermediate
  representation.

setup.py

@@ -175,8 +175,7 @@ setup(
         'alexa': ['avs @ https://github.com/BlackLight/avs/tarball/master'],
         # Support for bluetooth devices
         'bluetooth': [
-            'pybluez',
-            'gattlib',
+            'bleak',
             'pyobex @ https://github.com/BlackLight/PyOBEX/tarball/master',
         ],
         # Support for TP-Link devices