Add 3D Conebeam support

[hussam-stfc]

Desired Behaviour

Adding support for 3D Conebeam geometry.

This involves investigating what kind of changes are required. The Geometry object will need to be modified to support multiple geometry types. The CIL library might support this out of the box simply by passing it the correct Geometry type.

Potential Pitfalls or Risks to Avoid

Importance of Feature

Additional Context