Add a list-contents and get_by_name functions to the ws

[gonzalogacc]

A function to list all kmercount datastore names. This is required in some of the nodeview functions.

Something like

ws.add_kmer_counts_datastore("kmerds1", 31)
ws.add_kmer_counts_datastore("kmerds2", 31)
ws.add_kmer_counts_datastore("kmerds3", 31)
print(ws.kmer_counts.get_all_names())

Produces:

["kmerds1", "kmerds2", "kmerds3"]

[gonzalogacc]

And the same for counts inside de datastore:

ws.get_kmer_counts_datastore("kmerds3").add_count("pe1",...)
ws.get_kmer_counts_datastore('kmerds3').get_count_by_name("pe1")

Returns the entire kmer collection.

[ljyanesm]

This ticket also implements an "ls" function

[bjclavijo]

Closed by 92ed7c9