treenode.py: update the editor, not the user, when updating the confidence or the radius.
New class window.OptionsDialog to facilitate writing dialogs.
overlay.js: small fix, reduce scope of a variable.
tracing: new 'O' key binding for editing the radius of a treenode.
A dialog asks for the new value and offers options to apply
to the treenode only, the branch upstream or downstream, all the way to root,
or all skeleton treenodes.