Convert Rasa training data to new format

[amitkparekh]

Since v2, Rasa uses .yaml instead of markdown to store and structure training data. This looks to make the training more modular and should make things easier for new contributors. It can also help with #25.

More information on structure: https://rasa.com/docs/rasa/training-data-format#lookup-tables

Rasa have included an automatic way to convert old data to new, which would make life easier.