portal highlighter: shield+link mitugation
more tweaks to the request code
- delay briefly before retrying a timeout, and a bit longer before other errors
- also delay briefly before running the queue after a request, to give a chance of more than one request's requeued entries being handled atr once
- add a min tiles per request, to avoid sending multiple requests when only a few queued items remain
these are attempts to be nicer to the niantic servers, particularly in error cases, with some based on my best guess of the stock site behaviour, and others based on what seems reasonable to me