Improvements for this version:
1. Tweaks to built-in stylesheets.
2. Freewin window is deleted properly when host node is deleted.
#2 is a substantial improvement. Before this version, the situation where the underlying node was deleted was not handled at all. Deletion of the node could cause Leo to crash, especially if the node was later restored with a redo operation. Now if the host node is deleted, the plugin detects this and unloads itself in a controlled way.