Stone/gravel to salt (Overflow solution)

This is a solution to having an excess of stone or gravel constantly stopping production in facilities where it is a byproduct (especially ore processing facilities). The solution is to turn the stone and/or gravel into salt and ship this instead. This is especially useful for gravel, since it is rarely used in recipes, unlike salt, and salt is three times denser (TODO: check stack sizes to makes sure this is true - at the very least, 3 gravel turns into 1 salt). Stone is more often used, so it is preferred to turn it into salt only when there are overflow problems.