Voting calculation change

Right now, 4 of the equations are passed a witness `y` that we are voting on, but should instead be passed a creator ID `m`, whose witness is being voted on. For example, `vote(x,y)` returns a boolean for whether `x` is voting yes for witness `y`. That will be changed to `vote(x,m)` which returns the witness `y` created by `m` for which `X` is voting yes.  (Or `null` if it isn't voting yes for any witness created by `m`).  The switch will affect `vote`, `firstVote`, `copyVote`, and `decide`. In all those cases, we will have a parameter `m` (creator ID) instead of `y` (a witness).