Absolute read depth calculation

[AustinHartman]

This doesn't take all the long to compute, and can be useful information to know. Also, databases like GenBank require read depth/coverage when assemblies are submitted.

[AustinHartman]

Due to the reliance on assembly.fasta, read depth is calculated at the very end of the pipeline. Thus, the log header "Calculating read depth" and the depth information comes after the "Assembly complete" header. Maybe this behavior should be modified.

[AustinHartman]

Depth in the log will appear as
When long reads and short reads are available:

Calculating read depth (2020-07-30 20:36:55)
--------------------------------------------
Short read depth:   54.48
Long read depth:    22.88
Total read depth:   77.36

When only one type (long or short reads) are available:

Calculating read depth (2020-07-30 20:36:55)
--------------------------------------------
Short read depth:   54.48