Pre-UIP: Transparent Addresses

[hdevalence]

@cronokirby

First, I would suggest that for ease of use, we modify diversifier decryption in this case to always set the account index to 0, ignoring whatever encrypting the null ciphertext gives us. This avoids having the truncated address be pointing at some random account.

This is a great idea though and definitely we should do it. Only thing is we should think through the implications of having decryption no longer be bijective. I think this is OK since we’d never generate a t-address from an address index.