* Nest qbnewb under /modal to allow for other modals

move the api from api/user/:id/qbnewb -> api/user/:id/modal/qbnewb to
allow for the upcoming new dismissable modal

* Add additional datasetnewb route

staying with the same naming scheme as qbnewb. the db field is
is_datasetnewb, the route just takes datasetnewb.

I'm not wild about the default is true, set to false, and the naming
scheme. But will be easier to migrate and easier for FE to use if we
continue the defaults/logic etc.

* Remark on db change in migration file