binding group ignores widgets w/o data-bind attr

the `widgetize()` method instantiates widgets around stuff that either
has a `data-bind` attr or `name`, and `BindingGroup` only sets up
bindings for stuff with a `data-bind` attribute, so this ignores the
widgets that only have a `name` and no `data-bind` attr.
asWidgetizable `set`'s widgets, but not .widgets

before it was both calling `.set()` with a dictionary of widgets, and
also setting a `.widgets` property on the instance that was the list
returned by `widgetize()`. this was confusing, so now it just sets the
`asSettable` property.