fixes #62

The long-deprecated (since Ansible 2.4) use of include is
no more.

This is a simplification and a way to make it consistent with
how we do Postgres imports (see 6d89319822), using
files coming from the server, not from the local machine.

By encouraging people NOT to use local files,
we potentially avoid problems such as #34 (Github issue),
where people would download `media_store` to their Mac's filesystem
and case-sensitivity issues will actually corrupt it.

By not encouraging local files usage, it's less likely that
people would copy (huge) directories to their local machine like that.

This is a simplification and a way to make it consistent with
how we do Postgres imports (see 6d89319822), using
files coming from the server, not from the local machine.