Optionally report uncovered contigs in summary file

[dpryan79]

When processing large numbers of samples and storing the results for systematic comparisons it's handy to store results even for uncovered contigs. The .mosdeth.summary.txt file currently omits uncovered contigs. While we can easily program around that, it'd be super handy to (at least optionally) provide the entire set of contigs in this summary file regardless of their coverage status.