Feature/distribution sampling

[jwidauer]

Implemented the following functionality / features:

• The distribution_interface now owns an rng, which can be set and gotten externally and be used by it's children.
• Drawing a sample from a distribution is now a virtual function, which has to be implemented by every distribution (drawSample(...)).
• Drawing a sample from a Gaussian distribution is now implemented.
• Evaluating a pdf is now a virtual function to be implemented by every distribution (evaluatePdf(...)).
• Evaluation of the Gaussian distributions pdf, is now implemented.
• Evaluation of the Gaussian distributions pdf is also possible to be done in a vectorized fashion.
• Created unit test for distribution base class.
• Extended unit test of Gaussian distribution.