temperature parameter for metropolis coupling to model and SpExModel
Merge branch 'master' of https://github.com/macroevolution/bamm
Finish computeLogHastingsRatio function with temperature for Metropolis coupling

Implemented in Model.cpp, TraitModel.cpp, SpExModel.cpp, and the inline function computeLogHastingsRatio in Model.h. ALL log-hastings ratios to be processed by acceptMetropolisHastings should come through this function