demux_deplete: make depletion optional, load biosample metadata to tables

[dpark01]

This PR:

• closes #532 - percolates biosample metadata to Terra sample table in demux_deplete
• percolates more samplesheet metadata to library table in demux_deplete
• makes host depletion fully optional in demux_deplete (ie, works properly if all depletion database Array[File]s are empty / not specified)
• marks the terra.upload_entities_tsv task as volatile
• change default behavior of reports.align_and_count (used for spike-in counting) to only count proper primary mapped reads

The terra-specific bits have been tested live in a dev workspace.

[dpark01]

Ok this works and also as a side effect it restores the multi-library-merging functionality. It does have odd error modes if input tsv files are malformed--to do for a later date is to perhaps put some tsv validation / fail fast code up front.