Add workspace block type

[dnsosebee]

This needs more thinking-through.

But one idea is that: workspaces can go anywhere. workspaces apply to the parent block and all of its children, which cannot be overridden... workspaces appear in vertical order shown in editor.

[dnsosebee]

And workspaces automatically fold? / are significantly visually different? / don't have "numbers", instead have a bullet point that's outside the count? noice.