Stream-framework

- make add_to_storage signature consistent on all implementations (args and kwargs were missing for some)
- Add support for cassandra-driver 3.2.0+
- Use extras_require pip feature instead of custom install arguments

- Fix ignored redis_server timeline parameter

- faster deserialization for Cassandra feeds (skip ORM layer during serialization)
- optional cassandra install
- allow to use cassandra-driver v3 via install option

Breaking changes:
-----------------

Cassandra users:
* activity serializers now get a dictionary instead of a CQL model instances when loading data
* feeds' timelines that implements get_slice_from_storage now must return a dict instead of CQL model instance

- easier test setup
- add default protocol_version for Cassandra (v2)
- default serialization_id for aggregated activities is now with millisecond resolution
- add built-in sorting to Activity class

- support for using stream-framework with cassandra-driver 3.0.0. this enables support for cassandra 3.3

- update cassandra driver to 2.7.2