Support of new Kafka API and other minor improvements
A long awaiting support of kafka-python 1.x.x client. Now Frontera is much more resistant to physical connectivity loss and is using new asynchronous Kafka API.
Other improvements:
- SW consumes less CPU (because of rare state flushing),
- requests creation api is changed in BaseCrawlingStrategy, and now it's batch oriented,
- new article in the docs on cluster setup,
- disable scoring log consumption option in DB worker,
- fix of hbase drop table,
- improved tests coverage.