Toy MC trajectory depends on trajectory template

[brownd1978]

The ToyMC class is templated on the same trajectory as is used in the testing, and as such it fails when testing field effects on KinematicLine. It also makes comparisons between different helix parameterizations difficult to interpret. The ToyMC should use a fixed, well-defined parameterization, and FitTest should make comparisons only in terms of ParticleState.