Data loading and simple PCA plus plotting

This should be a starting point to load the data and do things funnier than a PCA later.

This file does the following:
    - globs the data that has been downloaded with datagrabber
    - excludes some faulty images (have a look at 96, 97, and 98)
    - as all the images are not full brain we cannot expect NiftiMasker to compute the mask or an extrapolating method to do anything sensible, so I took a standard MNI brain mask and gave it to the masker
    - a bit of work with the metadata
    - PCA + plotting, hopefully t-sne gives something better