Issue #561

Changes for issue #561 

NB.
- I am just now writing tests for my LayerController change. So please **don't do a merge** yet.
- I reformatted my code (whitespace, etc.) as I touched various files. These changes should be in separate commits so it might be easier to review commit-by-commit.


These changes include:
- The `WfsLayer` attached to a Layer now represents the layer to be used for WFS downloading. If you want WFS downloads off the same GeoServer that hosts the WMS layer then you need to configure a Layer to be it's own WFS Layer.
- I have included the names of the linked AODAAC products (which represent the download for ncWMS layers) onto the Layer edit screen. This means in once place you can see what downloads are available for a particular layer.
- There is now a separate template for the download view for data collections without a WFS or AODAAC download.