Removes unused imports in serializer, removes generic unit as it not
needed as though during planning process, removes getUnit from
simplestatenode now that is not being used. Checks to make test
serializer pass
Moves setunit and setscalefactor to SimpleStateNode from Avalue. Adds
setparent to AValue class. Updates tests with new output
Merge pull request #22 from openworm/review21

Moves setunit and setscalefactor to SimpleStateNode from Avalue. Adds
Merge remote-tracking branch 'origin/development' into replay

Conflicts:
	src/main/java/org/geppetto/core/model/state/visitors/SerializeTreeVisitor.java
	src/test/java/org/geppetto/core/TestTreeSerialization.java