Admin dashboard widgets used to require a size specification, telling

the widget that it's large or small. Small widgets were placed off to

the right, and large widgets were on the left. Large widgets weren't

really that large, and widgets that truly needed to be larger didn't

have a standard way of making this happen.
Now, we have a clearly-defined set of sizes that are based on column

widths. Default widget sizes now take 2 columns (the equivalent of

"large" before), while small widget sizes take 1, and large widget sizes

now take 3. This gives us a lot more flexibility in the kinds of widgets

we provide.
If they need something more custom (such as a 4 column mode), they can

use the #rb-ns-ui.admin.widget.set-colspan() mixin, which will compute

a proper size for the number of columns desired.
Widgets can also be set to full-width mode, which is 100% of the content

area.
In order to properly lay out widgets of various sizes, we now pre-sort

the widgets based on their initial size, placing larger widgets first

and smaller widgets last.
After any new layout computation, any widgets that had a change to their

width (such as full-size widgets, or any standard/large widget if the

viewport is too small) will have their updateSize() method called,

allowing them to recompute their size.
Unit tests were added to ensure that widget setup and layout ordering

was correct.

Tested that all current widgets look as they did before, meaning that

sizes and the new layout rules were correct.
Tested altering the sizes of the widgets in various orders to ensure

that the new layout rules were properly ordering the widgets from

largest to smallest, and that their orders were stable.