Add metadata for CSCL maintenance file geodatabase

[mattyschell]

We plan to add the internal "maintenance" version of CSCL to NYCmaps as a zipped file geodatabase. Add a single "maintenance cscl file geodatabase" entry to the metadata.

That entry should link to a page that describes the cscl geodatabase in full. List all layers in the geodatabase. In the future we may add additional metadata for these layers. For now the expectation is that users of this file geodatabase are already friends of CSCL and know what they are doing.