Rudder

Currently, everything on the relay stores data temporarily before sending it to another machine.
This make the infrastructure work even in offline mode.

However this feature has not been implemented in the shared-files relay API because of implementation difficulties.
But it should be implemented !

To make this happen, we need a temporary storage on the relay for those files.
We also need a way the signature validity of unknown nodes otherwise anybody could store anything on the relay.
We also need a permanent storage to store the metadata to check that a file is known (for the HEAD api)
Al last we need a way to clean this metadata storage if the real holder of the file doesn't have it anymore.