0029874: Visualization - capping plane transparency does not work

0029874: Visualization - capping plane transparency does not work

Interface OpenGl_RenderFilter and its implementations have been merged into OpenGl_Workspace.
This limits flexibility of interface, but simplifies logic.
- OpenGl_RenderFilter_FillModeOnly flag replaces OpenGl_CappingAlgoFilter;
- OpenGl_RenderFilter_NonRaytraceableOnly flag replaces OpenGl_RaytraceFilter;
- OpenGl_RenderFilter_OpaqueOnly flag replaces OpenGl_OpaqueFilter;
- OpenGl_RenderFilter_TransparentOnly flag replaces OpenGl_TransparentFilter.

OpenGl_CappingAlgo now:
- avoids redundant Stencil clearing when Layer contains at least one transparent Element;
- renders semitransparent capping plane within transparent elements pass.

vclipplane command has been extended by new argument -transparency.