No elements found when running an export process on a corpus

arkindex/workers/export!25 (comment 292121)

Since #1924 (closed), ListProcessElements returns nothing at all when there is no element and load_children is not set, because running a process on an entire corpus requires an additional step to ensure you really intend to do that. Export processes also rely on ListProcessElements, but creating an export process does not allow you to configure load_children, so an export process on a corpus fails because there are no elements to export.

When CreateExportProcess is called without an element_id and without selection set, it should set load_children to direct on the created process. This restores the previous behavior, when load_children was a boolean defaulting to false, causing only the top-level elements of the corpus to be returned.