Change "environments" to "frameworks"

This is more consistent with the language we're using at Stackbit, and it's more generally understood and consistent with the docs inside the section.

Address #33 first so that moving these isn't a problem. (But still put in redirects.)

Address issue #33 first, as requested. Then locate the website content using “environments,” replace the terminology with “frameworks,” and identify the redirects that must remain in place. Done means the relevant section and related references use the new wording without breaking existing URLs.

Written by the indexing model from the issue text.