R1:fa6a5a46ba57

Make more of the Calendar export workflow work

Summary:
Ref T10747.

- Adds a "Use Results..." dropdown to query result pages, with actions you can take with search results (today: create export; in future: bulk edit, export as excel, make dashboard panel, etc).
- Allows you to create an export against a query key.
- I'm just using a text edit field for this for now.
- Fleshes out export modes. I plan to support: public (as though you were logged out), privileged (as though you were logged in)…