Wizard support for vehicles related emission queries

Fixes #55 (closed) by adding wizard support for vehicles related emission queries and makes the platform more user-friendly.

• Adds the menu support which gives a list of categories for the user to choose one.
• Adds slot filling feature for Origin
• Adds slot filling feature for Destination
• Adds a list of Fuel Types
• Suggests parameter emission type and mileage.
• Adds support for both, querying directly and through the wizard system.
• Adds both comparative and number based response along with context-management support. Here's a preview of it:-

If the wizard-system is used

If the user queries directly