Implementing methods to deal with root keys

    - When extracting single objects, ED expects to be
      wrapped by a root key - issue 14
    - When sending data to the REST API, by default DRF expects
      the data without a root key - issue 15
Merge pull request #16 from holandes22/version-1.0

Implementing methods to deal with root keys
Update to latest ember and ember data.
Add integration test for getting lists of records.

This commit also includes the configuration for pretender.
A test for retrieving a single record.
Remove defaultSerializer from adapter.
Add test for creating a record.
Add test for updating a record.
Add test for deleting a record.