add custom demux settings for NextSeq, more stringent barcode Q score threshold for all systems but NovaSeq

[tomkinsc]

In WDL:

• raise minimum_base_quality for barcode matching to 25 except for NovaSeq
• increase max_reads_in_ram_per_tile and max_records_in_ram for NextSeq to account for larger tile size (avoid running out of open file handles)

In py tool defaults for picard:

• increase minimum_base_quality from 10 to 20 for more stringent barcode Q score threshold (while still allowing two levels of NovaSeq quality)