Boolean variable compression in SpecificationBlocks

src/main/java/avatartranslator/AvatarBlock.java

...main/java/avatartranslator/AvatarExpressionAttribute.java

src/main/java/avatartranslator/AvatarSpecification.java

...ava/avatartranslator/modelchecker/AvatarModelChecker.java

...ava/avatartranslator/modelchecker/SpecificationBlock.java

...ava/avatartranslator/modelchecker/SpecificationState.java

.../src/test/java/avatartranslator/AvatarExpressionTest.java