[FEATURE] Automatically added taxonomy layers to anvi-interactive collection mode

[meren]

The need

Collection mode serves as a way to display the distribution of each bin across samples (rather than contigs, which is the default mode). As highlighted in #1581 it would be useful to automatically add SCG taxonomy to improve that display.

The solution

Learn if SCG taxonomy was run for a given CONTIGS.db, initiate the SCG taxonomy class, update additional layers dict.

Beneficiaries

Those who use anvi'o collection mode to visualize their genomes across environments.