Include highway=track in trails layer by default?

[quincylvania]

Currently, we only include a highway=track in the trails layer if it has an access tag indicating someone has mapped it for some non-motorcar traffic. This nicely pares down the amount of data, but excludes a lot of ways that people would expect to see as trails.

It might be better to reverse the expectation, and include tracks by default to encourage people to put access tags on them.

This should probably only be done with #40, to make it easy to tell which paths are allowing motorized traffic.