Class represents an NLME Covariate parameter
Name of covariate parameter
Type of covariate parameter: Continuous|Category|Occasion
Curve fitting method: Forward|Interpolate|Backward
Is the structure diagonal (TRUE)| or box (FALSE)
Covariate centering value
Are the covariate values all positive
Type of value to use for the centering value: CovarNumber|CovarMean|CovarMedian
List of covariate effects
List of covariate items