UI for the new "Wikipedia" layout

[eomine]

@graphicore @dberlow

I've been working on mocking up the UI for the new "Wikipedia" layout.

Here's the Figma mockup. I've also exported it as an image and attached it below. I didn't mock up the inspector, but it should be similar to our current presentation of "Processed Properties".

I'm now wondering what else is missing:

1. I imagine there should be something similar to "TypeSpec Properties" to customize the heading and text styles?
2. Should column specs (min/max line length and gap) be customizable?
3. As discussed with @graphicore , justification specs should have another layout of its own.