Support for hexagonal pixels

[kif]

Requested by Eu-XFEL for this detector:

https://karabo-data.readthedocs.io/en/latest/dssc_geometry.html

[kif]

List of features:

• [x] Define the detector manually with 6 corners from an array of pixel coordinates
• [x] Define the detector automatically
• [x] Integrate without pixel splitting
• [x] Integrate with bounding-box splitting
• [ ] Integrate with full pixel splitting (4-corner pixel is hard-coded)
• [ ] Support 3D visualization in calibration