Detect running out of peers to buy from, or running out of money, report to user in callbacks.

[bedeho]

Related to JoystreamClassic/protocol_statemachine-cpp#1

Not only must it be possible to try again, rather than getting stuck as we are now, but some notification must be sent to the user, perhaps even at the operating system level, and perhaps also some sort of in app message queue which persists? (the latter is perhaps a bit too excessive, perhaps introduce in the future when we also have https://github.com/JoyStream/joystream-electron/issues/381)

[mnaamani]

Running out of Peers is fixed in #26