Calculate patient size and SSDE for CT AAPM TG 220 methods

[Ed McDonagh]

Refs #124 as both will require processing of all the image data.

See:

• https://gitlab.com/semps/openssde
• https://github.com/BwKodex/dicomimagetools/blob/master/src/dicom_image_tools/ct_tools/patient_equivalent_diameter.py

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[Ed McDonagh]

Not going to happen for 0.7.0