Use spins from cell instead of castep for UEP #80

[patrick-austin]

When loading for the UEP method, replace the spins from the castep file with those from the inital cell file. This propogates to the xyz files saved in the collection, and then onto the saved structures (if used).

Closes #80

[patrick-austin]

Following discussion with @leandro-liborio , have set spins to be zero instead of using the initial values.