Specifying histogram without bin edges causes error in aggregate

When running yori to grid files with a histogram specified using (start, stop, end) as opposed to (edges), an error is thrown when running the aggregate code.

This is because when the yori grid code sees a histogram specified without edges in the settings, it calculates the edges internally but never modifies the YAML string variable. That string variable is then written out in the gridded file metadata.

When the aggregate code reads the metadata, it cannot find edges and throws an error.