Added the LinearCongruentialGenerator class which is a 64bit random number generator that can be used to create reproducible parallel random number streams. It is based off of the MCNP5 random number generator. It is a very naive implementation and is therefore quite slow. It is configured to only be used when a MPI support is enabled and the system is build in debug mode. In release mode run jobs in parallel will only give reproducible results if the machine is completely homogeneous.