allow unfiltered queries to our internal db class
remove per-batch overwrite handling - that didn't actually work
add new `clear` phase to handle overwrite handling

this drops all data for a given day / source combination
first implemented for the SQL target plugin
gather all sources from any phase and remove data from targets

otherwise the ES target plugin would only be asked to remove data from the
`sql` plugin, but no entry actually claims this as its source
implement the `clear` method on two ES test mocks and correct test assertions