Improved train detection "algorithm"

[wissehes]

Improve the train detection.

• Compare the heading of the train with the heading of the user's device (maybe).
• Comparing the distance between the user and the train, to avoid showing a train that's >500m away as the current train.
• We can also compare the speed of the user with the speed of the train, for example to avoid showing a stopped sprinter as the current train, when we're actually in an intercity.

In this order:

1. Rank trains by distance.
2. Take the first 5 trains.
3. Make sure the first 5 trains are a maximum of 1km from the user.
4. Now sort by how close the trains speed is to the user's speed. So the first item in the list most closely matches that of the user.

And also adding a button for the user to understand why there's no train detected.

[wissehes]

A good first start would be to actually check whether the most close by train is actually nearby (<500m distance).

[wissehes]

Added checking distance in 4a3226b