how to account for non-oscillating plane

[mattsignorelli]

FPP accounts for longitudinal drift (RF off) with a special setting ndpt which treats the longitudinal as a parameter but must also satisfy poisson bracket (unlike the rest of the parameters which are just knobs). My current thinking is for NonlinearNormalForm to extend the Descriptor constructors to allow for this

[mattsignorelli]

Added field idpt in the maps which is Bool is the last plane is coasting, else Nothing if no coasting. idpt=true is the second variable in the last plane is constant (energy like) or idpt=false if the first variable in the last plane is constant