Support alternate (smaller) display for taxonomy levels with ancestor information

One consequence of the fix implemented in #487 is that it makes individual taxonomic classifications at each level much longer than before (since now we're including ancestor information). See the example screenshots below of the moving pictures tree, colored by Level 4 (order) taxonomic classifications.

| Old | New (#487) |
| -- | -- |
|  |  |

It's not a major thing, but some users might prefer the thinner legends in older versions of EMPress. Ideally, we would want to minimize the amount of text in each legend _while still preventing ambiguity_. I'm not sure of how to do this! (At least in a way that is both easy for users to understand and not super slow on the JS side of things.)

One potential solution that might work is trying to only show the lowest selected value (e.g. if Level 7 is selected, just showing species-level classifications -- e.g. `s__`), and only adding ancestor levels to the taxonomy string displayed in the legend as needed to disambiguate things. So this might look something like

- `s__coli`
- `g__Bacteroides; s__`
- `g__Lactobacillus; s__`
- `s__thermophila`
- ...

... That being said, mixing things up like this might confuse users more -- so I'm not sure.

Review the change in #487 and the moving pictures tree examples in this issue. Determine how legends can show shorter taxonomy labels while preserving disambiguation, then compare the result against the old and new displays. The issue does not name files, tests, or a specific entry point, so the implementation location must first be traced from the JavaScript visualization code.

Written by the indexing model from the issue text.