Add necessary utilities for generic translators

[AbeJellinek]

Replaces zotero/zotero#1656

[dstillman]

jsonld.js is this? Is this built fresh or just pulled from node_modules/dist/jsonld.js after an npm i jsonld?

In the Connector, do we know if this (large) file gets injected into each webpage/sandbox, or does it just get loaded in the background page/service worker? (@adomasven might be able to comment on this.)

[AbeJellinek]

Built fresh. I could add a script to zotero/zotero to do the build if you'd like. It's essentially just jsonld.js from the jsonld NPM package passed through Browserify with some very minor config changes.

[dstillman]

Yeah, for a large, modified third-party file, particularly one that has to be included in the browser extensions, it's better when we can point to a build script — e.g., so that we can point to that if a reviewer complains about it. (They really prefer unmodified files, but I guess that's not an option here.)

Should we just make the jsonld package a dev dependency of this repo and add a script to update the file? We're set up to do that in zotero/zotero, but the whole point of this repo and translate is to remove dependencies on zotero/zotero for translation stuff. zotero/zotero-build also has build scripts, but those are all for updating static dependencies in zotero/zotero. Probably clearest to keep this in one place in this repo?

[AbeJellinek]

OK, script added.