Cosmetics including address payable

[bokkypoobah]

@pertsev provided some cosmetic suggestions.

I will not be marking owner and newOwner as payable, as suggested, as the payable prevents an address variable from accidentally being used in a .transfer(...).

I will be leaving the address(uint160(owner)).transfer(...) casting in place, as this explicitly marks the statement where the transfer is made. For me, at least