racket/gui: fix problem with reparent and container sequences

In a container sequence, hides and shows are delayed, but
reparenting needs the hide operation to really complete.
mrlib/terminal: add options
GUI package manager: further refinements

Use better labels, such as "Available from Catalog" instead of "By List"
or "Do What I Mean" instead of "By Source".

Add filter box to the "Currently Installed" panel, andmake status marker
the same as on "Available from Catalog".