Added more tests with MuTalk

[DurieuxPol]

I applied MuTalk to add more tests.

testPackages := { 'AI-LinearModels-Tests' }.

analysis := MTAnalysis new
	            classesToMutate: {
			            AIAbstractLinearModel.
			            AILinearRegression.
			            AILogisticRegression.
			            AILinearRegressionLeastSquares };
	            testPackages: testPackages;
	            testFilter: MTFreeTestFilter new.

analysis run.
analysis generalResult inspect

This gives a mutation score of 91% (meaning 91% of mutants were killed).
I didn't mutate the manifest and the exception as they are not tested, and don't need to be I guess.
I also didn't mutate AILinearRegressionLeastSquares because it still doesn't work correctly in some cases, which I will investigate.