ConsensusProposal::changePosition

Update the position during the consensus process.

void
changePosition(
    Position_t const& newPosition,
    NetClock::time_point newCloseTime,
    NetClock::time_point now);

This will increment the proposal's sequence number if it has not already bowed out.

Name	Description
`newPosition`	The new position taken.
`newCloseTime`	The new close time.
`now`	the time The new position was taken