Implement Bremsstrahlung

[sethrj]

We're going to use the "simple" SB table (G4SeltzerBergerModel::SampleEnergyTransfer rather than G4SBBremTable:: SampleEnergyTransfer) for now: more complex sampler was introduced in Geant4 10.5.

• Import 2D physics vector (one 2D vector per element given to reader) Load Seltzer-Berger bremsstrahlung differential cross sections and store on device #186
• Storing 2D vectors on device Load Seltzer-Berger bremsstrahlung differential cross sections and store on device #186
• Sampling from 2D table for a given element (SBSimpleSampler) Add Seltzer-Berger energy distribution #204
• Sampling exiting brem photon direction Add Seltzer-Berger interactor and kernel #241
• Putting the pieces together: interactor (including additional constants) everyone including Add Seltzer-Berger interactor and kernel #241
• Integrate positron correction to cross section sampling (>10 GeV) Add positron correction for SB sampling #247

Defer:

• LPM correction (>10 GeV)