Design: "Export to PDF" Button in Export Cart

[danglorioso]

Describe the issue

Right now, it says "Export to PDF" as the blue button at the bottom of the cart dialogue. Really, it should say "Export All" to indicate to the user that one or more (multiple) figures are to be exported by this clicking this button.

Where Is the Issue / How to Recreate

Steps to reproduce the behavior:

1. Go to chart or heatmap page
2. Add figures to the cart via "Add to" button
3. See "Export to PDF" button at bottom

Suggested fix(es):

Update the text