Allow configuration of and/or event handling for web component from embedding page

[sHtev]

When embedding the editor, various options set externally may need to be set (e.g. menu selections), either statically upon initialisation or dynamically as the user makes choices on an active editor page. This needs to be passed to the bundled JS via some kind of configuration scheme, maybe similar to TinyMCE - https://www.tiny.cloud

To avoid reload/re-rendering, some kind of event handling may need to be included - this would also allow us to support buttons for running/remixing on the embedding page - this needs some investigation on how this can be achieved with WebComponents.

[patch0]

I think in the context of Astro Pi, we don't need to think about configuration too much (yet). I'm imagining delivering a component with a fixed configuration at first, so we don't need to enable/disable various menus.

[maddyjoe]

Our approach here is likely more important if/when we come to move away from using iframes for Editor in the context of Projects site (possibly CCW).