non-bcgw download duplications

[smnorris]

The downloads function creates a new folder for each layer.
For example, VQO gets written to the downloads folder 5 times.

[smnorris]

ebf3b2a ensures that the data only gets downloaded once, but as folders in source_data are named based on alias, a full copy of the source is still made for each layer. Some kind of folder name generation is required, concatenating url,file_in_url,layer_in_file