Sort and filter observation fields by count, place, and taxon

On the following changes.

1 - on the page add a column of data that indicates the number of observations which use that field
2 - Enable sorting on the page data table so you can sort by name, count (from above) etc
3 - Add the geography and taxa filters onto the page so you can filter the list to see which fields are used for a subset of data.

See related: