split up filters from plots and add tables to report

[kweav]

This PR is a ⚠️ stacked PR ⚠️ based on #33.

It addresses two of the next steps listed in that PR -- specifically it

• Include tables from the filters in the QC report so that users can make informed choices about which filters to apply
• Move the plasmid filter steps themselves out of the histogram plotting function into the R/02-filter.R file.

Adding to the next steps list, need to add functionality and reporting on whether both filters are used