Compute ETA on our own

[ckulfan]

So as we know, ETA is not published anytime soon after the boat departs.

• An alternative idea (and one that will allow us to calculate ETA when WSF goes down and we fallback to the 3rd party AIS API (likely https://aisstream.io/)), is to reference a lookup table that maps Progress to ETA. We know that via GPS we have a very accurate crossing percentage. So we should fairly easily be able to create a table via observation & logging.
• Perhaps we can even do the calculations between integers (interpolating?), so we don't need such a precise table.
• Obviously the boat accelerates and decelerates, but the table will reflect that.
• Perhaps there are linear or logarithmic maths that can be applied (not my strength).
• There would need to be a table for each route (duh).
• If we wanted to get real fancy, we could have sub-tables for the vessel classes (because they have different top/average speeds). So if Tacoma is on SEA-BI we'd apply the Jumbo MkII table.