Add Data tab to the extension

This is a work in progress to add a `Data` tab to the extension.

Main purpose is to display the defined models in the application, and adds the ability to view and inspect the loaded records for each model type.

- [ ] Add a Data tab to the extension which includes model types and records
- [ ] Add a data debug adapter to Ember core
- [ ] Extend the data debug adapter in Ember Data
- [ ] More test coverage for all of the above
- [ ] Design an icon for the data nav item