Add sliders to define min and max values

[cgsbob]

I would imagine that the Continuous Color renderer finds the minimum and maximum value from the Classification Field(CF) and renders the vector based on a linear interpolation of that features CF value. It would be great if a slider can be next to the min and max value color picker so that you can choose a different min and max. The slider should allow you to pick values between min and max and not allow the user to make min > max.