Added SemGenMenuBar and created seperate classes for the File and Tools
menu. Menu creation has been moved from SemGenGUI to those classes.
Created Observable class 'GlobalActions' to handle application level
requests. Classes SemGen, SemGenGUI and all SemGenTab classes now
implement Observer.
Added classes 'Workbench' to resource and 'AnnotatorWorkbench' to
package annotator.workbench. All model operations are to be moved there.