Source with angles as histo

[dsarrut]

Add an option to get angles from histogram for a source.

Warning : no test yet, no documentation yet.

https://geant4-userdoc.web.cern.ch/UsersGuides/ForApplicationDeveloper/html/GettingStarted/generalParticleSource.html

 source.direction.type = "histogram"
 source.direction.histogram_theta_weight = [0, 0.2, 0.6, 0.3, 0.05]
 source.direction.histogram_theta_angle = [
        20 * deg,
        45 * deg,
        90 * deg,
        110 * deg,
        120 * deg,
    ]
source.direction.histogram_phi_weight = [0, 1]
source.direction.histogram_phi_angle = [0 * deg, 360 * deg]

[dsarrut]

See #369