R1:9ab5f59ca23c

Export "date" and "remarkup" custom fields to Excel + "zip" extension check

Summary:
Fixes T13342. This does a few different things, although all of them seem small enough that I didn't bother splitting it up:

- Support export of "remarkup" custom fields as text. There's some argument here to export them in some kind of structure if the target is JSON, but it's hard for me to really imagine we'll live in a world some day where we really regret just exporting them as text.
- Support export of "date"…