chore (dashboardversion service): remove (one) join from store implementations
We return the userID from the dashboardservice store; the service (or api) layer can use that to get the user's login when needed.
The DashboardVersion struct is the database object; the DashboardVersionDTO is the object that should be sent to the API layer.
In the future I'd like to move DashboardVersion to dashverimpl and un-export it, but there are a few places that Insert directly into that table, not all of which are test fixtures, so that should wait until we clean up at least the DashboardService's use of it.
