This makes a few improvements to the item state support in list

forms, supporting some common patterns.
First, there's now a standard "error" state, used for items that have

failed in some way (useful for items that represent loadable things or

operations). This goes along with existing "enabled" and "disabled"

states, and has standard colors.
A new CSS class (djblets-c-config-forms-list__item-state), used for

showing a representation of an item state, has been added as well. This

makes use of a new registered text color code and icon provided when

calling #djblets-ns-config-forms.list.add-item-state().
This new class can be added to an item's template, and it will be

automatically populated with the correct text for the item. This involves

updates to the JavaScript support, which now uses an optional itemState

model attribute on the item. This will not only apply the new text and

icon, but it will also apply the CSS modifier class to the item itself.
This all results in a lot less that items have to manage. They no longer

need to compute their own CSS classes to define item states, or maintain

custom columns. They can just set an attribute.
Items that do need specialized CSS classes or text can override the

Djblets.Config.ListItemView.itemStateClasses and

Djblets.Config.ListItem.itemStateTexts to provide this customization.

Unit tests passed.
Updated the integrations support (not part of this change) and verified

all the state updating worked.