Completely redid how models are loaded and workbenches are created.
Workbenches are created via their respective factory, which loads files
and creates the SemSimModel which are then passed to the workbench upon
creation.
Tabs are created via the new tab thread which creates a separate Swing
thread for model loading and processing. Upon completion, the thread is
ended and the resulting workbench is passed to the new tab, which is
then added to the tab pane and displayed.