WIP: ENH: runTimePostProcessing - added option to clear/remove objects after use

When specifying line and surface function-object-based visualisation, use the optional 'clearObjects' flag to indicate that source objects should be removed/cleared after use.

Test case: cavity.tgz

Syntax:

    surfaces
    {
        cuttingPlane1
        {
            type            functionObject;
            functionObject  cuttingPlane;
            clearObjects    yes;              // new option
            ...

Note: only files that have been used will be removed, e.g. if a function object has created multiple surface files, unused files will remain at the end of the run - in the attached case the p surface remains...

src/postProcessing/functionObjects/graphics/runTimePostProcessing/CMakeLists-Common.txt

@@ -48,6 +48,7 @@ set(LIBRARY_OUTPUT_PATH $ENV{FOAM_LIBBIN}
file(GLOB SOURCE_FILES
fieldVisualisationBase.C
+    functionObjectBase.C
functionObjectCloud.C
functionObjectLine.C
functionObjectSurface.C