Issue #1 Improve performance for large java file (and large code bases) …

Fixed performance issue: the AggregateASTVisitor should only delegate to methods declared by the delegate visitors to avoid unnecessary AST visits.

AggregateASTVisitor.java:
Added methods analyzeVisitors(), isPrevisit2(), isVisit(), put(), getVisitors().
In main(), changed the code generation.
For all other methods, called getVisitors() to delegate only to methods declared by visitors.