Convert SQL data sources to return data frames.
Co-authored-by: Marcus Efraimsson <marcus.efraimsson@gmail.com>
Co-authored-by: Arve Knudsen <arve.knudsen@gmail.com>
Co-authored-by: Will Browne <will.browne@grafana.com>
Co-authored-by: Hugo Häggmark <hugo.haggmark@gmail.com>
