MRG: add additional weighted information to manysearch output

[ctb]

Addresses #380

Note: in #302, the meaning of 'query' and 'against' was flipped. For manysearch, unlike in gather/prefetch, 'query' is meant to be the genome and against is meant to be the metagenome. This PR switches them back, so that the mgmanysearch command line from the containment search plugin matches the manysearch command line:

sourmash scripts mgmanysearch --queries f_prausnitzii.sig.zip b_uniformis.sig.zip --against CD*.sig.zip -o search.csv

vs

sourmash scripts manysearch query.txt against.txt -o search2.csv -t 0

where query.txt contains f_prausnitzii.sig.zip\nb_uniformis.sig.zip (the genomes) and against.txt contains the CD*.sig.zip files (the metagenomes).

Using the display code in #380 to display search2.csv, we then get:

query             p_genome avg_abund   p_metag   metagenome name
--------          -------- ---------   -------   ---------------
B. uniformis        48.3%     2.0       3.4%     CD136
B. uniformis        62.6%    14.5      26.5%     CD237
F. prausnitzii       4.3%    24.7       2.5%     CD136

which matches the mgmanysearch output:

query             p_genome avg_abund   p_metag   metagenome name
--------          -------- ---------   -------   ---------------
F. prausnitzii       4.3%    24.7       2.5%     CD136
B. uniformis        48.3%     2.0       3.4%     CD136
F. prausnitzii       0.0%     0.0       0.0%     CD237
B. uniformis        62.6%    14.5      26.5%     CD237

[ctb]

@bluegenes this took me a minute 😆 . Let me know what you think!

[ctb]

Ready for review & merge!

[bluegenes]

you know, this direction makes a lot more sense. lgtm!