ENH: add pavian as a visualization option for Kraken 2 results

[misialq]

Currently, there is only one way to visualize the results obtained from Kraken 2 - taxa barplot. Also, this only works for reads (for now). It would be nice to bring in some more Kraken 2-specific visualizers which could leverage Kraken 2 reports directly and enable visualization fo results from both, reads and MAGs. One of such tools is pavian.

Notes:

• there seems to be conda package available on bioconda but only for Linux platform
• this is an interactive visualizer - would it be possible to pre-load our reports in the QIIME visualization directly? otherwise this cannot really work