Sheet preview

[cosme12]

Right now, the only way to preview the sheet while you are building it is by opening the html file and reloading.
A window displaying the actual sheet, after a "new block" is added, would be a great feature.

[JCharante]

I think that it'd be best to focus on / make this a subset of #11, as this issue will be resolved in the preview component of that issue.

I can't think of a solution short of hosting a local web server which is queried (or we could do a websocket server than sends a message to the preview page telling it to reload), but that might be overkill for something that will be scrapped when #11 is completed.