Design & implement RNG usage

[jared321]

@mosesyhc and I having been studying the current use of RNGs in surmise and developing an initial design of how RNGs should be used throughout surmise. In particular, we are taking into consideration the role and responsibilities of users in setting and using the RNGs as well as the impact that the design might have on the user's ability to control randomness in surmise and their subsequent analysis.

Finalize this design & implement. One main goal of this is be able to set the random seed of the RNG system such that tests run in each test setup can be run identically, which is a fundamental requirement needed for upcoming refactoring tasks.