BUG: fix translucency rendering of ruler

The subclass vtkAnnotationRulerRepresentation3D needed to implement
HasTranslucentPolygonalGeometry in order to have rendering triggered when setting
the opacity on the ruler label -this fixes the problem where when the opacity was
set to anything other than 1, it was not rendered at all.
Fixed other opacity and color issues on the 2d and 3d rulers to make them behave
similarly.
Note: the label visibility being on now shows tick labels in 2D, turning it off
will hide both the tick labels and the measurement label. Setting text opacity
to 0 will do the same thing.
TODO: 2D font size is not changing when change the text scale.

Issue 0003196

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24288 3bd1e089-480b-0410-8dfb-8563597acbee