add std::string Orientation::GetOrientation ( File *f ) method, that

add std::string Orientation::GetOrientation ( File *f ) method, that
computes the Patient Orientation relative to the image plane
from the 'Image Orientation (Patient)' :

           The first entry is the direction of the rows, given by the
           direction of the last pixel in the first row from the first
           pixel in that row.
           The second entry is the direction of the columns, given by
           the direction of the last pixel in the first column from the
           first pixel in that column.
           Anatomical direction is designated by the capital
           letters: A (anterior), P (posterior), R (right),L (left),
           H (head), F (foot).
           Refinements in the orientation descriptions are designated
           by one or two additional letters in each value.