Remove proposal from cascade example, improve error message.
Improve output, and shower diagnostics: hunting all the energy Produce REAL error message.

include proposal in build system
incl. proposal in cmake build. fix several problems.

There still have to be added multiple scattering effects and some deflections effects.
The directions and asymetrie of interaction products will be sampled.
There seems to be an issue with the particle cut or a implementation failure on proposal side that if a particle energy is below the cut energy, the particle is simply deleted without taken the particle cut relative difference into account.

The proposal library has to be installed manually and corresponding cmake variables have to be exported.