++++++++++++++++++
**Updates**
- Add fields to MapLayerMetadata object
- llbbox - lat/long bounding box
- map_image_link - link to a png image
- download_links - other download links for a WorldMap layer
- download_links - dict of links to export in different formats:
- [u'zip', u'gml', u'tiff', u'KML', u'jpg', u'json', u'pdf', u'csv', u'xls', u'png']
- .zip is shapefile, json is geojson, tiff is geotiff
- Remove field from MapLayerMetadata object
- datafile_id - not needed. Field is part of the token.
- Source data at WorldMap only needs a Layer object to produce MapLayerMetadata
- Share MapLayerMetadata object and related form code in Geoconnect and WorldMap
- added index to DataverseInfo.datafile_id