Mobile Layout Support for Dashboards

__Proposal:__
Dashboards should layout in a useable way on mobile and desktop. I understand some users might just make separate desktop and mobile dashboards, but it would be nice to have an option for better layouts on quick and simple dashboards. I would propose something simple, like giving the user an option to change the fixed gird size on mobile. If seems like the current grid is 12 cells, it would be nice to maybe have mobile wrap cells down, for a fixed size of 3 or 4.

Alternatively, giving users the option to enable horizontal scrolling might also be nice. So users can still see the same fixed-width view as the desktop, without the graphs being squished to nothingness.

__Current behavior:__
If you make a dense dashboard on desktop, with cells in the 2-3 width range, on mobile the cells are so squished in the width you can't see the information in them.

__Desired behavior:__
I had a few ideas described in the proposal.

__Alternatives considered:__

__Use case:__
Making dashboards and being able to check-in quickly on mobile.

No files, tests, or entry points are named in the issue. First locate the dashboard layout implementation and its responsive-layout tests, then clarify whether the desired result is wrapping, a configurable grid size, or horizontal scrolling before defining completion criteria.

Written by the indexing model from the issue text.