Combined update

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[mrtcode]

The overview of the most important changes made to arkivo, zotero-api-node, stream-server.

arkivo

• Implemented a reliable resubscribe, resync logic which also resulted in various Arkivo architecture changes. The main idea is that what it does on restart and what it does on stream-server reconnect is basically the same except that on restart it firstly finishes the unfinished jobs. Now it has a consistent and predictable main loop.
• Now Arkivo firstly subscribes to stream-server and only then does the sync. Previously it was opposite which could result in missed updates and not triggered sync.
• No more waiting for stream-server responses to return success/failure to client on subscription creation. Instead we just simply request the provided items URL with the key, and then check the response. Previously it was not returning any response if stream-server was restarted.
• Handles zotero-api-node stream errors and doesn't crash on various connection errors.
• Increased versions URL limit to 5000 which makes library sync much faster.
• Fixed a bug for plugins that use a callback.
• Solved node_redis deprecation warnings.
• Added support for relative plugin paths.
• Documented Arkivo re(sync), stream re(subscribe), subscription creation and removal flows, which will be helpful for further development.

zotero-api-node

• Now always reconnects, if zotero-api-node errors are handled (by Arkivo).
• Disabled resubscribe, because it has bugs and architectual issues.

stream-server

• Returns an error event instead of closing connection and killing all other subscriptions.