consider relays or buffers based on availability #18

Example : a mobile devices relies on a desktop to realize demanding tasks, e.g generation or STT. One can be on while the other is off, and vice versa later on. Consequently the task can never be completed in a properly distributed fashion. Meanwhile, some devices, e.g NAS or IoT gateway, are 24/7 on. They are though not always available if being used on another network.

Provide a mechanism to provide devices as optional relays or intermediary nodes, able to store files and unfulfilled requests for others. It can be done explicitely, while setting up a node, or self discovery by checking availability periodically, see /available.