The function modifies the zoomX, zoomY,
panX, and panY so that all elements of a particular layer are
displayed.
l_scaleto_layer(target, layer)either an object of class loon or a vector that specifies the
widget, layer, glyph, navigator or context completely. The widget is
specified by the widget path name (e.g. '.l0.plot'), the remaining
objects by their ids.
layer id
l_layer_ids