measure width directly from map imagery

[andrewharvey]

The width preset should have a ruler/tape measure button, that when clicked will let you measure a distance on the map (with aerial imagery as the reference) then the distance should be rounded based on a reasonable precision based on the zoom level that the distance was measured at.

[mxdanger]

In addition to that, it would be nice if the width and other related attributes on ways could be visualized.