Make RegressionCurveHelper more readable (com::sun::star -> css)

Change-Id: I9b9e63a81bf5002413d18267b1000230f9ca7cdd
RegressionCurveCalculator & co - com::sun::star -> css

Change-Id: I7cbf11009b5d7dbe2464288e696a1fcb1f3de3a0