Feature/map color by

This adds and implements drop-down selectors for changing map feature color and size by field.

According to @kshepard, the map is only to show data for 2013, so the table name shouldn't need to change.  I'm considering building the CSS out of color ramps and value ranges, in which case I may parameterize the table name as well.  I don't know if it make sense to pull in another module just for the table name, though, especially considering that the column names don't appear to be consistent across the two years we have.