Add the missing test baseline comparisons

There are a number of tests whose output is not yet being compared to a baseline, e.g. `itkFFTPadPositiveIndexImageFilterTest`.

The tool could be improved by steadily adding the baseline images to the corresponding folder, and add the `--compare-MD5` flag with the appropriate arguments to the corresponding test in the `CMakeLists.txt` file.

I may be able to help with the task.