Data reorganization

[rvosa]

The data folder needs to go. Roughly the following needs to happen:

• GIS data are 3rd party assets. They go in some ephemeral, local folder that we don't advertise to the outside world.
• Occurrence data go in a shared folder structure where we can access them internally, e.g. a dropbox or google drive. We embargo them for now.
• Species lists, traits, are in https://github.com/rvosa/sdmdl-angiosperm-data
• To the extent that this folder is now a template (or example) for users to run their
  analyses in, this folder can perhaps live on inside 'docs'.

[rvosa]

The data folder still needs to go. I think this folder is now limping on multiple ideas:

• initially we were stuffing data for the use cases in here. That was clearly unworkable
  because (1) it needed too much space, (2) the use case data are not of interest to
  potential users of sdmdl. Following that reasoning the folder can simply be deleted,
  just like we have been planning to do subsequent to this issue and our announcement
  to this effect in the root level README.md, where we say the folder is marked for deletion.
• however, this folder is now coming back in by the backdoor as, essentially, a template for
  for users to run an analysis in. This is a reasonable idea, but if this is basically an example/
  template folder, then the logical thing to do would be to move this folder structure inside
  docs so that it automatically becomes part of the documentation system.

[rvosa]

Current status: we are going to see in the Usage example of the documentation how this folder structure is deployed by users and how it functions in their analyses.