Part Dimension: alterations to existing files

    Not sure what is happening with View3dInventorViewer.h.
    The only REAL change, beyond the addition of dim functions, is
    the removal of the member arrowrotation. It wasn't referenced anywhere.
Part Dimension: new implementation files
Part Dimension: new icons
adding some headers
fixes for windows
adding toggle and clear to context, view menu
Merge branch 'refs/heads/tanderson-rev-partdimension'
additional places for measurement commands