#544 Improvements to Deviate objects

This PR hits two small issues related to Deviate objects:

- (Issue #544) Added the ability to use all of our various Deviates in config.  They are called `RandomPoisson`, `RandomBinomial`, `RandomWeibull`, `RandomGamma`, and `RandomChi2`.
- (Issue #537) Changed the behavior of BaseDeviate when lseed=0 to try to use /dev/urandom for the seed rather than the clock.  This should be a better source of random bits.