Suggestion: Make package display tree more nested

[snunez1]

The packages browser is great, but at least on some systems, very, very long. It would be helpful to perhaps nest it a bit more, so that, for example, you might have:

alive
debugger
errors
eval
file

with only alive at the top level and the subsystems visible when expanding the tree.

There's no standard way of naming these package, but for the last few years ASDF has recommended using / as the separator. With that and . as heuristics, we'd probably get most packages properly structured in the tree.

Same for ASDF SYSTEMS pane.