Add select all/none button for taxon selection

[nbokulich]

Improvement Description
taxa selection is currently primitive. I like the function, but it needs to be expanded to allow select all/select none (probably as a single checkbox), and by default should be "select all" so that clicking on individual taxa removes them one by one rather than isolating that specific taxon and removing all others (following my suggestion, the current situation would be replicated by unclicking "select all" and then click the taxon of interest).

Current Behavior
Currently, if I want to view all taxa but a few, I need to manually click through a long list. Select all/none would make it much easier to eliminate or focus on a select few.