Support insert_all/3 with source

[rschooley]

https://hexdocs.pm/ecto/Ecto.Repo.html#c:insert_all/3

It expects a schema (MyApp.User) or a source ("users")

I only see tests and an implementation for passing a schema to insert_all/3 in ecto_mnesia.

[AndrewDryga]

Yes, we have noted in the readme that we don't support schemaless queries. I plan to work on adapter during next few weeks and going to take a look how to support them :).