Arrival times can differ due to clock sync issues

[onebusaway]

Arrival times can differ due to clock sync issues

[paulcwatts]

I've been looking into this, and I may just end up punting on it and going with #27 instead. There's no way we will be able to get sub-minute accuracies. There are so many larger fish to fry.

[barbeau]

I was looking at this again in context of trying to debug some potential differences we're seeing between predicted times and vehicle positions, and trying to eliminate device/server clock sync as a potential source of differences.

One catch is that we can only use the server "current time" if we just recently had a successful refresh of the arrival info data from the API. There are several locations where we potentially use a cached response, and in those cases we should still use the device current time (as the "current time" of the server will be old).

[barbeau]

WIP PR at #484.