Return parsed items in results for all umm_json* formats

Currently, only format `"json"` will cause query results to be parsed into individual items. All other formats are returned as entire pages, requiring the caller to parse pages of results.

Short of more comprehensive support for all (or most) query formats, at the very least parse all umm_json* formats, so instead of returning a list of _pages_ from a query, return a list of the _items_.