Allow charge decorated supercell structures (No change to API) (#141)

* make element_change more general

* grouping and plotting

* minor changes to plotting

* update supercell algo for charge state

* update supercell algo for charge state

* update supercell algo for charge state

* updated supercell

* Failing test for locking

- test_substitution fails with sc_pos at sub.site # array([0.333333, 0.666667, 0.37588 ])

* shift by frac_coords

* fixed test for plotting

* fixed test for plotting

* undo thermochanges

* old thermo

* complex equiv test

* latex test