[NEW] moving average aggregator

[Domeshow]

This is a new aggregator which gives the moving average as the values ​​are linked. It does not take empty cells into account.
Let me explain.
Since the moving average can be calculated for any period, this aggregator calculates the moving average over the previous periods. So the more the table increases, the more the period increases.
This is in draft for two reasons:

1. I still need ideas because I wonder if it should be done over a fixed period (of 3, 5,..)?
2. The script should be in CoffeeScript as stated in the guideline but I'm having trouble converting this code to coffescript.

[marclaporte]

This is a good start!