bob.core.random has many classes for different data types

Created by: siebenkopf

Having a look at the bob.core.random module, I can find several bindings of classes for different data types. Instead of having all these classes, I would suggest two solutions:

1. We have one class for each distribution type and a dtype-like parameter for the constructor.
2. We have only one class overall, having the dtype and the distribution type as parameters.

Either of the solutions will break the API, but I think we should avoid these data type specific classes and functions. In C++, these classes are templated, anyways...