Refactor DataFlowAbstraction so that it has only two fields: statement and variable

[pauloborba]

 private Local local;
 private JInstanceFieldRef localInstanceField;		     private JInstanceFieldRef localInstanceField;
 private JArrayRef localJArrayRef;
 private StaticFieldRef localStaticFieldRef;

[barbosamaatheus]

Currently at #31 I add the attributes:

private Statement stmt;
private Value value;

However, an effort is needed to refactor the other analyzes that still use the other fields. In a quick analysis, I believe only intra OA analysis that uses these fields.