Add rate limiter to imports

[mirka]

This adds rate limiting to the CoreImporter so that we don't have to rely on the hacky workaround in nudgeUnsynced to get large imports unstuck:

simplenote-electron/lib/utils/sync/nudge-unsynced.js

Line 42 in 0b079b9

client.client.connect();

With my new familiarity with the LocalQueue 😌, I was able to realize that the stuck import notes were not stuck locally, nor were they being "ignored" by the server. They were sent out correctly, but then each of them were being returned 503 errors from the Simperium server.

@roundhill:

• Should node-simperium be patched to handle these errors?
• Should there be an official rate limit for the Simperium API? (In this app, I set the limit to 250 requests/sec. It is a little conservative, but I think it's fine because according to Tracks, imports larger than 100 notes are very rare.)

To test

1. Set localStorage.debug="sync:*,analytics" and reload.
2. Import a file with >500 notes.

The syncing should complete, and nudgeUnsynced shouldn't log anything other than 0 unsynced notes. (Or, you can try commenting out the client.client.connect() line quoted above.)

Import file (1000 notes) for your convenience: few-tags-1000-800kb.json.zip

Next steps

Now that this is out of the way, I will modify the nudgeUnsynced function so that it specifically addresses the v === 0 notes that resulted from unpersisted offline changes (#1098). We'll get rid of the client.connect() call there, thus fixing the init flood once and for all 🔨

[roundhill]

As discussed in Slack, let's set MAX_REQUESTS_PER_SEC to 50.

[roundhill]

Filed Simperium/node-simperium#70 for our friend node-simperium.