Adjustable taxonomy browser layout

[JWCook]

Widgets should be better able to make use of available screen space. For example, depending on screen size:

• Taxon ancestors/children can take up too much vertical space
• Taxon search and/or tabbed lists can take up too much horizontal space, if you're mainly interested in the selected taxon info

Possible solutions:

• Improved custom flow layout and dynamic widget sizing; lots of fiddly manual work, difficult to get right
• Collapsible panels; this would be ideal, but QT doesn't appear to have any built-in features for this
• Dock widgets
• Splitters; not quite ideal, but may be the easiest option

Update: Apparently, splitters are better than I thought. They allow completely collapsing widgets on one side of the splitter or the other, as long as the child widget sizing policies allow it.