Corrects lack of step size scaling in adaptive burnin
Fixes improperly loaded settings for cluster.starting values
Removes McmcApplication as a superclass of MpiMcmcApplication

This was no longer an accurate relationship, and it had caused at least one bug (scaleStepSize bug).

Removal was trivial, with a slight bit of extra handling (with Knuth's multiplicative hash) for the mt19937 generator being all that was needed.