Updated SimulateCKD to working state.  Warnings still present

Details
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* Added class parameter checking in SimulateCKD
* Clarified calls to be pass by named parameters in mdply calls
* Fixed GenerateBaseCoef in glg class
* added residual.parameters class to return value of ResidualParameters
* fixed tests.
Merge branch 'refclasses' of github.com:jennyteng/CKDsim into refclasses

Conflicts:
	R/CKD_simulation_main.R
	R/slope.model.constructors.R