Blocks that can generate multi-column and series layouts

So we can quickly define pages like this without needing to create or modify a template:

| - 25 - | --------- 75 -------- |

| - 25 - | ---- 50 ---- | - 25 - |

| --------- 75 -------- | - 25 - |

| ----- 50 ----- | ---- 50 ----- |

I tried a version of this a few years back, but it was an overly complicated solution.

I think there's a simpler approach that just manages the page structure as a simple Javascript array of rows with a few properties like:

Style, a class to apply to that row for styling (can we make this selectable from classes in their stylesheet if they follow a convention?)
Background image selector (popup over page and change in place)
Layout, column configuration based on admin/util/minimal-grid e.g., "25,50,25", "33,66" (selectable but preferably visually represented)
Columns (array), each column is just a block of HTML you can edit (we can streamline this for common things like inserting photos later)

We can serialize that to a new JSON field in the database (mediumtext?), probably in Blocks.

Could we also use filemanager/photo to let people choose a full-width background image for a whole column?

jbroadway / elefant