Introduce the concept of PhaseParameter

[Ipuch]

Introduce the concept of PhaseParameter.

The idea is to declare a phase parameter to be able to map them.

The core idea is not to be able to map parameters except if they are phase dependent.
If they are not phase dependent, this is the responsibility of the user to use the parameters multiple times in its dynamics.

Time would become a phase parameter.
It would be beneficial for @Kev1CO to implement magnitude of fes or implement width pulse.
It would be beneficial for the VariationalOptimalControlProblem, too, to be able to declare multiphase problems.