Fix moving average - backwards looking instead of forwards looking

[koenkuhnkoon]

The moving average is currently the average of three time points T, T-1 and T+1. It should instead be calculated from T, T-1 and T-2, so we don't lose the most recent year of data (to avoid the impression that the data are old).

[koenkuhnkoon]

This one is important and I hope it can be done before public release, given the interest in 'recent' data.

[tonyfujs]

Fixed by commit 4ec50d