Add ability to create a "data upload directory" location for projects (ie. the related project "root" dataset.)

General stories to break down: Add file(s), remove file(s), replace file(s).

Other notes and ideas:

Add link "enable upload directory" to list of Admin functions for project.
Constrain location to reasonable file system locations.
Add configuration parameter to differentiate deployments for "root path".
Provide reasonable default paths.
Review whether this is required for children datasets of project (note file clobbering issues.)
Beware uniqueness limitations in paths of files uploaded.