Implement interface to access Session Context

[dariowho]

AS A framework user
IN ORDER TO access dialogue session easily and uniformly across connectors
I WANT TO use a standard interface for session contexts and parameters
INSTEAD OF accessing the native Dialogflow data within predicted intent

Details

When a service, such as Dialogflow, predicts an Intent it typically keeps a conversation session with context information. In Dialogflow, this is mainly

1. The list of active contexts and their remaining lifespans
2. A list of intent parameters and their matched values in the conversation.

We want to study a way to generalize this information across different services (Alexa, Azure, Wit.ai, ...) and provide a common interface for accessing it through the Intent class (as well as referencing context values in language resources). A specification for this is to be defined.

Test Scenarios

TBD

[dariowho]

Solved with the more abstract concept of "relation": Intent class member that reference parent/related intents along with their parameters and lifespan (see #7)