Remove duplicate particles [feature request]

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#1

Hi,

Would it be possible to add an option to remove duplicate particles during particle extraction? I would suggest adding a duplicate removal threshold, where if two particles are closer than x Å after recentering, only one is kept. This would be useful when re-extracting particles in a smaller box after initial classifications have been performed in a larger box, where there is some risk that two initially mis-centered picks may end up converging on the same particle after recentering.

Cheers
Oli