Statistmo format and itkStandardImageRepresenter does not handle TransformMatrix

[marcelluethi]

Some medical image formats, such as mha or nifti allow for the specification of a transformMatrix (or direction matrix). If an image with an explicit transformMatrix (which is not the identity) is used as a reference for building an image or deformation model, this information is lost. The resulting samples from the model will not be in the same spatial position as the specified reference.

The bug can be easily reproduced by loading an .mha image whose TransformMatrix is not the identity.

A solution to this problem requires a change in the statismo file format as well as the different representers.