Improved initial defect structures through ShakeNBreak

[jkshenton]

Getting initial muonated structures to screen using e.g. DFT is currently accomplished using either the UEP, AIRSS-like approach or using high-symmetry sites (is that correct?).

I think it would be useful to add in support for the functionality in ShakeNBreak (https://github.com/SMTG-Bham/ShakeNBreak) to allow users to quickly screen different initial configurations for the same site - by modifying bonds etc - see the paper for more details. This would provide a much more robust muon stopping state finder. i.e. not just trying out different initial muon positions, but also different muon+crystal configurations.