[WIP] Fractal with bconds rcnstrct from 2dx

[pdziekan]

Like fractal reconstruction with bcnds, but here reconstruction is done not from the scales of dx, but from 2*dx, i.e. every second resolved point.
NOTES:

• each thread needs at least 5 points along y axis, compared to 3 in reconstruction from dx (this could be fixed by making some threads not reconstructing at all, it's a matter of refinemenet_ranges)
• in PBL this approach gives more (too much?) energy in smallest scales
• in UWLCM this gives larger spread of th and rv within cloud