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

Add deflection caused by scattering. Scattering along the track is not yet possible because the track is a const object.

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.

Add basic Python package skeleton.

See merge request !256

Update corsika data

See merge request !264

Resolve "ParticleCut doesn't affect "non-secondary generating" processes"

Closes #200

See merge request !261

Resolve "Unable to find boost"

Closes #306

See merge request !260

Resolve "Add histogramming functionality"

Closes #33

See merge request !259

make functions inline, otherwise the linker complains

See merge request !262

Resolve "update shower animation script"

Closes #232

See merge request !255

Update boost to 1.74

See merge request !251