Use generic Data<'T> type for deserialization of templates.
Split Grammar and Templates

* Moved Grammar to its own namespace and file
* Moved templates to their own files in a Templates folder.
* Merged WebApp and Vega.
* Added script for the arc template
* Included an additional generic parameter for the Range field.

NOTE: Arc does not currently render.
Fix issues with the Arc chart.
DU based representation with Basics