Adding functionality for multivariate normal distribution
Merge branch 'development' of https://github.com/revbayes/code into development

Conflicts:
	src/gui/Source/Views/AnalysisView.mm
	src/gui/Source/Views/ModelView.mm
	src/gui/Source/Views/NotebookView.mm
	src/gui/Source/Views/RbView.mm
	src/gui/Source/Views/SimulateView.mm
	src/gui/Source/Views/TreeSetView.mm
	src/gui/main.mm