Cell2Particle Attributes

This Pull-Request removes the nice "one-particle-view" in the functor called by `Cell2Particle` by transparently giving in the `frame` and the `particleID` the functor should work on.

This has the major advantage to enable the use rvalue attributes like getCharge, getMass again. Furthermore, re-writing the whole particle in a MapTuple and writing a *second interface* on *how to access particle attributes* is not a good idea at all, sorry.

I am sure we can re-implement a "single-particle" kind of scope/view when René got his *flex-particles* ready.