Change client-side notion of selection.

Now, selection is built into the State:
* documentListParams: filter, a (new immutable class) DocumentListParam
* oneDocumentSelected: if true, one doc; otherwise, the entire doclist.
* documentId: iff oneDocumentSelected, the one doc

Now we can toggle oneDocumentSelected. [finishes #62348706]

Other bugs reside, but I don't think there are new ones.