[Feature Request] Grid Layout - allow grid items with different sizes

[ciampo]

It seems that, at the moment, all grid items need to have the same size.

I think it would be useful to allow custom grid layouts, for example:

Is this this something that can be achieved easily?

[Westbrook]

I also love this idea! I've been in the code a bunch and know it wouldn't be immediately easy. However, I wondered what it might look like with the v2 class notation to have a structure whereby there was a baseline iron-list element that offered easy hooks for extenders to instill some more custom layout methods. Seems like it would go great to simplifying the grid vs not grid code, surfacing something like the above, as well as other layout like horizontal scrolling and things not yet talked about in the realm of this component.

I use iron-list a lot in my work, and would be super pumped to help out in any way if that (or something similar) seemed like a smart way forward, @blasten.