ENH: add the ability to propagate pixel types for App. Add propagation as...

Closes #11 (closed)

Changelog:

• add the ability to propagate pixel types for App, as optional argument propagate_pixel_type. Add propagation as default behavior for Slicer and Input
• add a to_numpy(propagate_pixel_type=False) methods for all pyotb objects. This method is also called by np.asarray()
• fix the order when using slicing for ROI selection. Before, pyotb was following numpy convention, i.e. obj[rows, cols]. Now, pyotb follow the obj[x, y] which is more adequate for geoghraphic selection
• fix the pyotb.get_pixel_type function