support czi zstack and time points

Caller needs to calculate the correct index for osr->levels array as:

Let z, t, c be the z-stack index, time point index and channel index,
respectively. And let

Nz: total number of z-stacks
Nt: total number of time points
Nc: total number of channels
Nl: total number of levels

index = z * Nt * Nc * Nl +
             t * Nc * Nl +
                  c * Nl +
          level_in_channel

Signed-off-by: Wei Chen <chenw1@uthscsa.edu>