Adapt state for SOACollection based tracks
This adds q/p to the state definition for track classes based on the SOACollection.
In principle one would like to not have z in the definition (as it is not a continuous variable), but I would not know how to do that with the SOACollection (and memory wise it might not matter). If anyone knows I am glad to hear about it.
It also adds a StateParameters enum, such that one does not need to write numbers by hand anymore for the coordinates, i.e. StateParameters::StateVector::x is to set the x coordinate of the state.
Proxies for states_field, state_cov_field and vec3s_field are adapted to only accept enums. The store function in the SOACollection is adapted to also accept enums (but not enforcing it so far).
Also introduced a new structure pos_dir(s)_field to have a "state" without q/p, e.g. for VeloTracks.
Deprecated the set method for the states_field as the order of arguments could be ambiguous.
Changed StatePosition(s) to State(s).
Needs: Rec!2574 (merged)