TFC Weather 1.6.8

Reworked algorithm for filling barrels during rain. Frequency and attempts can be configured.
Reworked sand and snow layer logic, now both more optimized and improved the logic for where the storms can deposit sand or snow. Max depth and layers are configurable.
Added snow dunes to world gen for new chunks, making smooth terrain gradients. (Configurable)
Fixed TFC snow and Vanilla snow from not melting if below trees, as that prevented snow from melting when summer arrives