Node labels don't currently make use of the 'align' property, so this reuses
the existing property.
The label code has a number of alignment options that make sense to edges only,
so the Edge/Node now passes a boolean to the Label ctor to explain which the label
is being rendered for
Will only apply to Network nodes with a shape: 'box' property, as most
other shapes this will not make sense for. This enables the box shape
to be used, for instance, for diagraming CFG data from source code.