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

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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.