Abbreviated transfer as one event

I removed the POA experiment from my other transfer PR, trying to create a fairly vanilla version of transfer that moves beyond give-Transfer-receive. I tried to do the minimum that would basically work, and that I hope we can more or less agree on as a direction. And that is better than what we have. I think there will be a lot of situations where this is plenty.

Note that currentQuantity is possessed quantity in this PR. So there may be a gap in reporting a standard balance sheet, but it could possibly be figured out with some digging into agreements. And is probably less important at the moment.

@elf-pavlik do you think this is getting close to something we can start to move forward with?