Fix #309 with better obfuscation of private info (paths)

This MR implements the following changes:

• DatasetManager now has a obfuscate_private_information static method that takes as input a list of dicts, each dict representing the metadata of a dataset, and returns the same list but modified to obfuscate private information (for now, only paths pointing to locations on the node)
• in the future, it will make more sense that each data type implements "how" to obfuscate this information. Since now it is really simple, the implementation is directly within the DatasetManager's function
• The node calls this obfuscation function for every search and list request it receives

See #309 (closed) (especially the first comment) for a discussion. The current implementation is better reflected in this diagram