Admin: coverage edit 2: permanent polygon data, with passenger route toggle

This is a major redesign. The existing design holds only one set of data for each map, just the current set of polygons that comprise the coverage. Once a polygon has been deleted, it's gone entirely - a line deleted from the coverage map can only be reinstated by manual GIS work, or by regenerating the map from scratch, which would lose all the other changes. My proposed design would provide a "base" map, with polygons covering the entire network in the relevant country or region. The coverage editing tool would then allow each polygon to be toggled as included or excluded for the coverage map. As with the existing tool, it would be possible to select multiple polygons and toggle them together.