Add wrapper around qdyn_prop_traj with mesolve interface

[goerz]

It would be nice to have a routine in qdynpylib with the exact interface of qutip's mesolve. It would use the existing LevelModel to write a config file and runfolder based on the given QuTiP objects, then invoke qdyn_prop_traj (which should probably be renamed to qdyn_propagate at some point), and lastly read the resulting data and return it in the same format as mesolve would. This would allow having a workflow were a "toy model" could be explored in QuTiP before switching to QDYN for a larger system where QuTiP is no longer numerically feasible, without writing any new QDYN-based Fortran code.

I already have an implementation of such a mesolve wrapper in some of my own project codes. It is not fully general yet, but the missing parts are relatively minor.