Fix state share copy to clipboard in insecure context (http)

[RussTorres]

Using the "Share" button to post to a state server on an http deployment on most browsers will send the correct request, but quietly fail copying the link to the clipboard because the navigator requires a secure context.

In this commit I introduce a function that replicates the original behavior in the secure context, while providing a workaround when the original method would fail. I also modify the returned link to include the pathname, which I believe was leading to incompatible copied links when being serving on a subpath.

It's not uncommon to want to stand up http versions of neuroglancer to talk to custom state servers or view local http data sources -- I think this makes deployment easier for those cases and hopefully eliminates some confusion -- let me know what you think.

Thanks!
Russel

[fcollman]

You might want to resolve this with #789

[jbms]

Thanks for looking into this. There is an existing method in src/util/clipboard.ts --- does that solve this problem?

[RussTorres]

Thanks @jbms it looks like setClipboard does solve the copying problem -- I didn't realize this was already implemented.
Adding a commit using that. It still looks like the pathname addition to link is a required addition on some deployments.

[jbms]

Please fix the lint error. Thanks

[jbms]

there are still formatting issues --- note that you can run those tests locally to speed up iteration