Django-ethereum-events

The events that are monitored are now provided by the database backend and not the settings file

**Proof-of-Authority** networks are supported by setting the ``ETHEREUM_GETH_POA`` setting to ``True``.

Package is now compatible with web3 v4. As a consequence, the following have been removed:

- Python 2.7 compatibility
- Python <3.5 compatibility

Changed the log fetching method from using ``web3.eth.filter`` to processing each block transaction by hand.

This fixed the following issues:
1. Multiple address monitoring not working with Ganache
2. Multiple topics from the same contract not getting retrieved

Merged changes from drdaeman