Storage providers

[Ryccoo]

Integrate a persistent (preferably) storage into charyf-core.
Should be configurable the application config.

It is important to define the outer contract so different implementation can keep it. The base contract should define a key value storage.
Key should always be string.

Value may be an object

• it is important to determine how to implement for instance redis like storage -> Object should support to_json method then.

[Ryccoo]

In memory-storage provider is available now, which is sufficient. May require a redis version to persist data for production.

Memory providers are used for internal parts and strategies -> app code should be handled on its own. For now, message IDs are mainly stored to avoid dispatching the same message twice (facebook interface sends the message again if it does not get response correctly in time)