throw exception when transaction amount is 0
don’t log tx status changes if status hasn’t changed
[#452] fixed senderHash/targetAddress confusion

since the first version of Hive, senderHash stored the source address
for incoming transactions (until it was removed), and the *target
address* for outgoing transactions; this has caused much confusion and
some incorrectly saved or displayed data

the property was now replaced by sourceAddress and targetAddress, which
work pretty much as you’d expect (except sourceAddress is empty for
incoming transactions right now)
[#453] fixed contact matching for incoming txs