ENH: First test is added

This test needs three input argument: fixed image, moving image and the
baseline image all from the BRAINSTools test data.

It runs 4 stages of registration, and itkTestDriver is used to compare
the output moving resampled image to the baseline image.

Many function definitions that are common between different tests are
put in one file (TestFilesCommonCode.ipynb), and this file is run at the
beginning of each test using ipython magic functions.