Add alternative map view to datagrid

[trife]

1) attempt to utilize position_coordinate fields to generate gridded field map 2) if position_coordinate fields are empty, prompt user to select x and y axes from ObservationUnitProperty headers. Update observation_units table with their selection (both type and coordinates)

[trife]

For imported fields, if/when users select this option on the datagrid toolbar, the field creator UI for assigning x/y positions to each plot can be reused.