Procgen trees - dynamic wind

Did some more work on procedurally generated 2D trees.

I added a new tree type, firs, and added dynamic wind that rustles the trees softly when idle with randomly varying strength. You can also create stronger wind by pressing NUM7 or NUM9.

Also added the ability to manually stretch or compress the height of a tree without changing the scale by holding down ALT while planting or pressing NUM8 or NUM2. It deletes the old tree and generates a new one of the same type at the currently selected height.

Next I'll be adding more complex trees with separate branches, starting with pine trees.