0031729: Visualization, Prs3d_DatumAspect - provide per axis text aspects

0031729: Visualization, Prs3d_DatumAspect - provide per axis text aspects

Prs3d_DatumAspect::TextAspect() now takes Prs3d_DatumParts argument
and defined separately for Prs3d_DatumParts_XAxis/Prs3d_DatumParts_YAxis/Prs3d_DatumParts_ZAxis.
The method without arguments has been marked as deprecated.

V3d_Trihedron now stores per-label text attributes.
Added method V3d_View::Trihedron() returning V3d_Trihedron object for more straightforward definition.
V3d_Trihedron::SetWireframe() - added missing invalidation.

AIS_Trihedron::setOwnDatumAspect() implementation has been moved to Prs3d_DatumAspect::CopyAspectsFrom()
and now used by Prs3d_Drawer::SetOwnDatumAspects().
OpenGl_Text::render() - added NULL-check.

AIS_Trihedron::computePresentation() now takes into account Prs3d_Datum*Arrow shading/line aspects.

Command vtrihedron has been extended by "-textColor XAxis|YAxis|ZAxis Color" syntax.
Command vviewcube has been extended by "-xAxisTextColor|-yAxisTextColor|-zAxisTextColor" arguments.