Resolve "Alignment: missing focus calibration"

The current alignment routines do not offer support for computing important parameters used for calibrating:

• the camera focal distance.
• the scintillator tilt with respect to the camera focal plane.

Closes #135 (closed)

The implementation requires the following steps:

• Translate option 'std' of https://gitlab.esrf.fr/tomotools/octave_archive/-/blob/master/m/tomotools/focus.m#L348
• Translate option 'angle' of https://gitlab.esrf.fr/tomotools/octave_archive/-/blob/master/m/tomotools/focus.m#L272
• Create unit test with sample data, and expected values
• Implement fit plotting
• Produce docstrings