#18 MCWF_Trajectory state-vector caching

[Vukics, András]

A "basic" MCWF_Trajectory should also be provided which cannot undo steps and hence doesn't need state-vector caching.
Common code is to be factored out into a common base class.

The user then needs to know whether there is a lot of serious dplimit-overshoots in his application (by looking at the log of some example trajectories), and decide accordingly.