improve terrain view move to: rotations uses TerrainCamera, try to keep constant frame rate
rename vector mapping related classes (don't limit to "surface mappings")

VectorsToSurfaceMapping -> VectorMapping
VectorsForSurfaceMapping -> VectorMappingData
AttributeVectorMapping -> PolyDataAttributeVectorMapping (this uses the centroids!)
don't require vtkPolyData in VectorMappingData
remove scalars from RenderedData while hiding the object
handle vector mappings in RenderedData base class
RenderView: remove data from UI components before deletion
add line/lined arrow representations to VectorMappingData
add lineWidth, color to VectorMappingData interface, emit geometryChanged() only when changing values in the UI
move vector mapping from RenderedVectorGrid3D to Grid3dVectorMapping
obsolete SurfaceNormalMapping