Rename layer one,two,three to alpha,beta,gamma

[Stentonian]

The reason for not using 1,2,3 was so that we don't have names like layer_1_1_sig. So instead we used one,two,three. But these do not align in order when you do alphabetical order. We could use a,b,c but single chars may be mistaken for other things, so alpha,beta,gamma seems best.