Make sure that EasyCloud is not affected by error issued by some measures stores (e.g., connection refused by a Redis server, etc.)

Specify what version of Kafka/Redis (both server and python bindings) classes have been tested. Other minor changes

Added 'from_conf()' method in the base measures store class as a abstract class method to make sure that measure stores subclasses implement it

Added framework for storing measures, including CSV-based file store and a stored interfacing with Apache Kafka