data_model config files should be optional

[robsavoye]

If there is no data_model for the specified category, there will be no data extract at all. In this case a dummy data extract should be created that consist solely of the centroid of the project AOI. Otherwise ODK Collect won't launch. Right now if there is no data returned from the query it already generates a dummy file, so this should just be a conditional that works without a data extract produced by an SQL query.

[Samtoosoon]

hey please assign me the issue