Include number on csv download action, download selected

Before, download as csv downloaded everything. Now it will only download selected, noting the number that will be downloaded in the actions menu.

This requires the explore template to have certain marker spans, such as "collection" and "document" in order to download the correct things. That is a requirement if a template uses the result--holder.

Similarly, a span with the class "num" needs to be in the tool configuration for additional tools for the tool text to update.

These things will be documented in a later commit!