adding same reflection should be ignored

[prjemian]

When a user creates a file that is reloaded many times, such as during development, it can lead to the same reflections being added multiple times. We should handle this case more gracefully than to simply accumulate additional reflections.

Example:

• fourc = Fourc(...
• select_diffractometer(fourc)
• new_sample(...
• add_reflection(1,1,2, ...
• add_reflection(-4,0,2, ...

These would be in a example.py file that is reloaded with %run -i example.py

[prjemian]

This would be enabled in a Python reflection class with a dunder equal method:

def __eq__(self, other):
    return comparison_result