Format field in the catalog

[m-mohr]

There's a format field in the catalog. It lacks documentation and it is not clear what exactly should be included there. Is it the union of all formats that are available throughout the items/assets? The example names "cog" and "geotiff", but who standardizes these names? Users may also use MIME-types or file extensions.

For example GeoTiffs could be referred to as:

• tif or tiff (file extension)
• gtiff (GDAL short name)
• geotiff (somehow self describing name from the example)
• image/tiff, image/tiff;subtype=geotiff or similar (MIME type)
• cog (arbitrary names of special GeoTiff flavors)
• probably more

[m-mohr]

Seems to be related to some discussions in #54.

[m-mohr]

Removed with #175.