Renamed sigmoid GUI params

src/consts.cu

@@ -49,6 +49,6 @@ void copyConstantsToDevice() {
 
 // ----------------------- TransferFunction -----------------------
 __device__ float d_opacityK;
-__device__ float d_sigmoidOne;
-__device__ float d_sigmoidTwo;
+__device__ float d_sigmoidShift;
+__device__ float d_sigmoidExp;
 __device__ int d_tfComboSelected;