Cloudio-endpoint-python

- Fixed exception bug in endpoint class

- Updated to `cloudio-common-python` v0.3.0

- Updated homepage link

- Added a thread to `CloudioEndpoint` class to decouple MQTT client calls
- Removed Python2 support
- Reformatted code according to [PEP 8](https://www.python.org/dev/peps/pep-0008/)
- Extended `CloudioAttributeListener` interface

- Bugfix in attributeHasChangedByEndpoint() with PendingUpdate
- Python3 compatibility

- Small improvements and bug fixes