More notebook updates

[jbednar]

• Fixed misc minor issues with Viewing_AIS
• Merged AIS_Drilldown into Viewing_AIS (and deleted it)
• Created AIS_categories.csv with Vessel_Type and category information
• Added environment.yml used in the Viewing*.ipynb notebooks

Note that Viewing_AIS uses the vessel type/category information, but it doesn't currently work, as these files have categories like 1004.0, not 32. AIS_Drilldown didn't work for category either, as it always reported Unknown, so this is not a regression. For now the type name lookup is commented out in Viewing_AIS, but @jlstevens may be able to figure out the mapping and re-enable the number to type name conversion.

[jlstevens]

Note that Viewing_AIS uses the vessel type/category information, but it doesn't currently work, as these files have categories like 1004.0, not 32.

I also noticed this and I've been assuming this is due to corrupted data. Unfortunately, I have no idea how these numbers >1000 are supposed to map to the actual AIS vessel types. This is one reason the categorical datashading example is in zone 10 where the vessel types make sense.

[jlstevens]

The issue with these categories is about to get fixed in a new PR using data from here