Further sensor API support (#4)

* Sample further sensor API support

* Fix typo (battery, not batterylevel)

* Remove unused import

* Implement more sensors

* Remove conversions and units of measure

* Add switch button constants

* Implement switch button constants

* Fetch properties from raw instance variable

Also, only use 'get' if a property may not exist in the API result.

* Fix buttonevents for ZLL switch

* Fix/add CLIP sensor types

Also, reorganize ZGP Switch into a single class (as there is only one ZGP Switch, it doesn't currently make sense to have a Generic ZGP class and then a ZGP Switch class as we can't really be sure what the base ZGP properties would be).

* Add sensor types to example.py

Provides examples of the properties exposed for each sensor type.

* Add missing property decorator

.gitignore

@@ -5,3 +5,5 @@ pip-selfcheck.json
 pyvenv.cfg
 dist
 aiohue.egg-info
+.DS_Store
+.idea