Allow to identify a boost/stream; clarify uuid

[joksas]

Currently, the description of uuid seems ambiguous—it is not clear whether the payment refers to the one made by the listener or the one sent out the individual recipient. Podverse and Podcast Guru interpret it as the latter.

Anyway, identifying the boost or stream by the listener is still useful. For example, suppose there are feed recipients Alice and BoostBot, and, during a value time split, another feed is referenced with recipients Bob and BoostBot. BoostBot is likely to receive two identical TLV records (except for uuid). It is then not clear whether to count this as a single boost or two boosts for analytics' purposes. Looking at the splits and the timing of the payments, it's possible to make good guesses, but none of them are foolproof.

Therefore, I'm proposing boost_uuid, which uniquely identifies the payment made by the listener.

Here's the pseudocode of how apps may handle it:

boost_uuid = new_uuid()

for recipient in recipients:
  recipient.tlv["boost_uuid"] = boost_uuid
  recipient.tlv["uuid"] = new_uuid()
  send_payment(recipient)