User configuration of UI

[IanMayo]

Once we've got browser storage sorted (#11), I'd like to let users change the UI.

Here's the flow:

• at app load, we populate the UI using example.js
• we also store this UI into local storage.
• We have a config UI button. This lets the user produce an editable copy of the current UI. The user specifies a name for the new UI
• Then the UI definition is made editable via the JDorn JSON Schema Editor (https://github.com/jdorn/json-editor)
• This takes the UI schema file, plus the current UI definition
• On complete, the UI switches to use this new one
• Alternatively, the user can switch to any other user-edited UI layout.