Slight refactor for using the last-run URI
Using _default_config for hashable data

element.config (dict) is easily modifiable by the user, so it should
really not be used for building the hashable config object.
Setting a default parameter savefile name

Doesn’t appear to work on my mac, but maybe it works on other platforms?
Correctly loading container collapsed status
Fixing issue with programmatic collapsing

When a container is collapsed pragmatically, it now ‘manually’ ensures
that connected elements have their visibility set accordingly.  In
practice, this proves to be more reliable than the system of callbacks
in this circumstance.