Find way to warn on marker maps that locations are scrambled

[grassick]

There is a concern that maps made from scrambled data (see mWater/mwater-forms#187) will stigmatize other households or will appear to show incorrect data as points will be in the lake, for example. We need a way to include the fact that the geometry is scrambled in the schema and then bubble that up to a warning in the map when the zoom level is sufficiently high.

This should only be used for marker maps and cluster maps that use exact geometry locations. Where the warning should appear is up for discussion.

If the messages only to appear above certain zoom levels, then the information in the schema should include the maximum scrambling radius.