BoFiN: Tidied imports, removed redundant things, added pad_csr function for RHS construction
BoFiN: Tidied imports, removed redundant things, added pad_csr function for RHS construction

A raft of updates:

1)  Added time dependent Liouvillians to fermionic case

2) Added optional resturns to fermionic run function

3) tidied up imports

4) removed redundant variables and parameters (nhe, _N_he and total_nhe were all the same thing,  there was a redundant graph plotting function we didnt use, etc).

5) when constructing L_helems we were directly filling elements in ranges.    Quick test showed that this was very inefficient compared to the old pad_csr stuff alex made, so I switched back to that.

cgranade/qutip,qutip/qutip,cgranade/qutip,qutip/qutip