FIX - sort pyramid members by product of scale factors when creating / adding new pyramid member

[Bang Pham Huu]

Currently, when creating / adding new pyramid member, it is always pushed to the top of the pyramid list.

It is fine as this is the common way to build pyramid from high → low resolutions. (e.g. Sentinel 2: 10m, 20m, then 60m)

However, if one wants to add a pyramid member in the middle of the pyramid, this is not correct (e.g. Sentinel 2: 10m, 60m, then 20m).