:list renderer in klein.Plating should support dictionaries, and fill slots with their values

Use-case: we have a list of things which have a display name, an interesting attribute, and an internal ID. We want to render something like <tr><td><a href="id">display name</a></td><td>interesting attribute</td></tr> for each one - a pretty standard list view.

Problem: right now each element in the list is just filled as the item slot, which means in order to accomplish this we need to build a separate widget.

Suggested solution: if klein encounters a dict, instead of doing fillSlots(item=_extra_types(item)), it should do fillSlots(**item); then the template for the list can be self-contained.

Start from the :list renderer and the existing fillSlots(item=_extra_types(item)) behavior described in the issue. Update dictionary handling so its entries become template slots, then verify that a list template can render each item's display name, attribute, and ID without a separate widget.