Rationalise coxphSLMAassignDS and coxphSLMADS

[tombisho]

coxphSLMAassignDS is designed to store a Cox model on the server side (assign) and coxphSLMADS is designed to return a summary of a Cox model (aggregate)

The only line that should be different is 207, where one returns the summary and the other the complete object.

There are some other differences, though, around these lines:

	    control <- gsub("~ bbbb", "", control, fixed = TRUE)
	    control <- gsub("~", "", control, fixed = TRUE)
	    control <- gsub("bbbb", "", control, fixed = TRUE)     

compared with:

control <- gsub("~bbbb", "", control, fixed = TRUE) 

I think this second one will miss ~ bbbb

Also in terms of maintainability, there should probably be a single function that generates the Cox model and applies the disclosure control (this might be called coxphSLMADS). Then there should be two other functions for the aggregate and assign operations, that call the main function. The aggregate would just call the main function, then do summary() on the coxph object and return to the client. The assign just returns the coxph object which stores it on the server side. That way the bulk of the code is in one place.