Avatar Model Checker: adding optimization on empty transitions

src/avatartranslator/AvatarElement.java

src/avatartranslator/AvatarSpecification.java

src/avatartranslator/AvatarStateMachine.java

src/avatartranslator/AvatarTransition.java

src/avatartranslator/modelchecker/AvatarModelChecker.java

src/avatartranslator/modelchecker/SpecificationState.java

src/ui/window/JDialogAvatarModelChecker.java