Major redesign of how PrintObjects are loaded

With the new ability to have a print queue the old method of handling
the loading of print objects was extremely inefficient and awkward.
This loads PrintObjects into an ArrayList in the JobExecPanel itself so
that the MachineSimDisplay only handles the loading of a single object
at a time.
Added more Data to PrintObject

PrintObject now stores more information about the object itself being
loaded

This makes the loading of multiple objects much more convenient because
all of the information needed to load the object is stored together with
the object.