Re-think metadata output

[sckott]

Right now, we output one list of metadata for each data source. However, any number of API calls are made for different combinations of user inputs. I think it makes more sense to have each of those requests have it's own metadata output, each output can have different results and different inputs.

Probably retain the single metadata list for each source as a summary

The new setup potentially:

(out <- occ(...))
gbif --- |
         | -- meta # global metadata for gbif output
         | -- data --- | # output for each API request/species/geometry set
                       | -- sp1 -- | 
                                   | -- meta # metadata for single request/species/geometry query
                                   | -- data # data for single request/species/geometry query
                       | -- sp2 -- | 
                                   | -- meta # metadata for single request/species/geometry query
                                   | -- data # data for single request/species/geometry query
                       | -- ... and so on
bison...
ecoengine...
...

If changes made, of course affects downstream methods, need to fix those too