example hubs don't go to a good location

[daler]

Each of the example hubs that demonstrate the different kinds of track types have data that are on different chromosomes. These should either be moved (e.g., by downloading the example tracks, converting to plain text, manually editing them to be in the same genomic region, and converting back to big* format) or the example hubs should be edited to include a relevant default position.

The latter can be worked out by looking at the table schema for a track to see which chromosome at least the first data point is found on, and then zooming to an appropriate region from there.