Mmmonk feedback: Improve word choice for import/export flow

[marlo-longley]

This report by Mmmonk is based on feedback from 300 users. One finding is that technical language throughout the app is making users uncomfortable and confused.

Here is the suggestion from the report for the import/export flow:

Use 'save collage' instead of 'export', and 'open saved collage' instead of 'import'? When the user clicks on 'save', provide a non-technical explanation on what to do next. E.g., "It is not possible to store your collage on this website. But you can save your work by copying and pasting this bit of code into a document on your computer. When you want to return to this collage, click 'open saved collage' and paste the code into the provided area." Something along these lines could work to guide less confident end-users?

Broken out from #3906