Better job retry, code quality

[dumbledope]

Better backoff and retry logic for some worker jobs:

• The balances job runs less often (now every 5 minutes)
• The finalize jobs retry every 10 minutes, and retry for more instances, to account for expected block times and confirmation delays

Various small fixes regarding code quality:

• Instead of checking for undefined with typeof val === 'undefined', added isNullish and isNotNullish helpers that check against null and undefined
• Removed unused imports and variables