ENH: cache flushing for changing nibabel version

This implements flushing the joblib cache if the nibabel version changes. Indeed, there is an internal structure of the Nifti1Image that changes across the different versions, and this gives rise to incomprehensible errors.

The behavior can be turned off.

Cc @AlexandreAbraham : I think that you should review this, as anything that gets close to cache is dear to you :)

Closes #139