Added new Input and Output nodes.

The new Input and Output nodes are very similar to dot nodes.
They form the interface to groups.
For a given group you can only see these nodes when viewing the
contents for the group.
The InputNode has no visible input plug, as it connects to something
outside the current group.
The OutputNode has no visible output plug either, as it also connects
to something outside the current group.
The intersting thing though is that input plug and output plug of the
InputNode and OutputNode respectively will appear on the group node,
when viewing the contents of the surrounding group.
This is important when constructing the input plug or output plugs of
InputNodes and OutputNodes respectively because the GeoLoader used to
construct the input or output plug will not be the same GeoLoader as
that used for the node.  In fact it will actually be the GeoLoader of the
parent group of the group node to which the Input or OutputNode belongs.
However the Input and OutputNodes will use the GeoLoader of it's immediate
parent group like all other nodes.

Input and Output Nodes have a trapezoidal shape, tapering up or down.
These emphasizes the fact the data is flowing into or out of this group
via these nodes.

A new trapezoid shape has been added.
Entities, PackedShapes, and Drawables have all been added for these
new InputNodes and OutputNodes.