Adds ACR Uniformity functionality

[YassineAzma]

Resolves #188.

• Adds an ACR uniformity script that calculates the integral uniformity of slice 7 of the ACR phantom. The methodology is as follows:
  • Calculates the centroid of the object following morphological operations and a centre-of-mass calculation.
  • Small circular masks, corresponding to an area of 1cm² are generated at a dummy location, which in this case is the centroid.
  • This circular mask is then translated around a large ROI, corresponding to an area of approximately 200cm² offset from the top of the phantom, and mean values for each position are calculated. There is an exclusion criteria on small ROIs where some values exist outside of the large ROI.
  • The small ROIs containing the maximum and minimum mean values are used to calculate the integral uniformity.
  • These results are visualised in the report, as shown below:

• Contains an initial attempt at unit test.
• Associated modifications to init.py to add the necessary hazen task.
• Added Siemens test data to the tests directory.