Add a List widget that implements Editable and other useful traits

[ulyssa]

It would be useful to have a widget similar to the List widget in the tui crate that implements the following traits:

• Editable to support moving the cursor using EditTarget values
• Jumpable to support moving back to previously selected list items
• Promptable so that list items can be selected
• Searchable so that it plays nicely with non-EditTarget searches
• Scrollable so that keys that scroll the viewport without necessarily moving the cursor work
• WindowOps so that it can be used with WindowLayout