Option to call without chunking

[glennhickey]

As discussed in #737, chunking along path ranges looks to be more trouble than it's worth on the cactus yeast graph.

• It is brutally slow with the recall-context size of 2500
• The nodes are so small, that it's possible that insertions are still missed
• The resulting chunks (I think do to all the dangling ends) are very slow to compute snarls on (I measured 2 hours for one chunk, vs 6 minutes for the entire input graph)
  So the idea is to get an option to disable chunking altogether and just run vg call on the input graph.

[glennhickey]

@cmarkello replacing len(bed_lines) with chunk_counts[chunk_bed_chrom] here fixes a bug where the last overlap/2 bases of all but the last chromosome get clipped out when the input gam wasn't split by chromosomes. Mentioning because it may affect your wdl script.