Failing API calls (spotbit.info/api is offline): Update CCXT and improve error handling  #105

The https://spotbit.info API is offline.

As noted in #103 (comment), Spotbit is currently crashing because API calls to exchanges are continuously failing.

The result is that either API calls fail immediately or, when attempting to get results for a range of dates, Spotbit keeps trying until it runs out of memory. The system then kills Spotbit. Restarting Spotbit then causes the same error.

We should:

• Update to the latest CCXT which hopefully reflects whatever changes have occurred with exchange APIs.
• Improve error handling so that Spotbit immediately stops retrying when unknown errors occur. That is, if an error we don't specifically handle occurs then Spotbit should always fail and report that error instead of attempting other requests.
• Blacklist failing exchanges and report them for the Spotbit administrator to manually verify the bug.