Back button should take user to previous page instead of homepage in some situations

[unicorn-utterances]

Back button should take user to previous page instead of homepage in some situations

[crutchcorn]

I admittedly thought we had a story for this. Unfortunately, that's a bit complicated.

We'd need this to be merged first:
reach/router#197

Otherwise, trying to add location.back would hard reload the last page which would break a lot of transition functionality/etc

[crutchcorn]

I found an issue (now that reach/router#197 was merged) where navigation from gatsby doesn't allow -1 to be passed (the back command) due to it's query parsing. I am trying to talk to the Gatsby team about opening a PR myself to fix this issue, but have gotten stuck on a technical issue and am awaiting a reply from them. More as this develops

[crutchcorn]

gatsbyjs/gatsby#19044 we're now waiting on this