Wrong imports in dt5

[jjgomezcadenas]

In dt5.ipynb one finds the code:

import pytomography
from pytomography.metadata import ObjectMeta, ImageMeta, PSFMeta
from pytomography.transforms import SPECTAttenuationTransform, SPECTPSFTransform
from pytomography.projections import SystemMatrix

All import fail, apparently they refer to an obsolete installation.

The same occurs in dt6.ipynb