0028004: Visualization, AIS_ColorScale - allow defining labels list not equal to...

0028004: Visualization, AIS_ColorScale - allow defining labels list not equal to intervals list

Cosmetics, code clean up.

AIS_ColorScale now draw labels using Graphic3d_VTA_CENTER
vertical alignment flag, instead of incorrect own alignment logic.
The color bar now adds margin on the top simmetrical to the bottom.

AIS_ColorScale::SetSmoothTransition() - added new property
for displaying colorscale with smooth transition between color intervals.

AIS_ColorScale::SetHueRange() - added new property defining the hue angles
corresponding to minimal and maximum values on the color scale.

AIS_ColorScale::SetLabels() now allows setting the sequence of free labels,
which number does not match the number of intervals.
In this case the labels will be displayed at positions of virtual
intervals corresponding to the number of labels.