Add support for required parameters

[gdaniel]

We need to provide support for required parameters that are filled with additional questions by the bot.

[gdaniel]

This feature is tricky to implement: we need to see how the DialogFlow Api answers incomplete queries and check if this is a feature coupled to the DialogFlow console.

If DialogFlow sends a custom response for requested parameters then we can probably adapt the framework to take it into account (or at least provide an "intent" connector to the designer). If not we need to reimplement it on the Xatkit side.

[gdaniel]

We need to handle this at the core level too

[gdaniel]

Required parameters are not part of the next release (current release: v1.0.0)

[gdaniel]

Required parameters are under discussion for the new language.

[gdaniel]

Required parameters are not a construct in the new language, but they can be easily simulated with transition conditions and/or if statement in state's body, e.g.
Transition condition version

MyState {
  Body { }
  Next {
    intent == MyIntent && intent.context.get("context").get("parameter") !== null --> NextState
  }
}

If statement version

State1 {
  Next {
    intent == MyIntent --> CheckState
  }
}
CheckState {
  Body {
    if(context.get("context").get("parameter") !== null) {
      // do something
    } else {
      // print an error message
    }
  }
  Next {
    // return to the previous state to wait for the intent again
    context.get("context").get("parameter") === null --> State1
    // continue the execution, the parameter is set
    context.get("context").get("parameter") !== null -> NextState
  }
}