Add automatic dependency retrieval for JarFileCreator

This improvement sets the package of user code as default package and let user to specify additional packages to be scanned.
Tested with inner class, anonymous class and additional package.
The current API could be used like: 
```
JarFileCreator jfc = new JarFileCreator(jarFile);
jfc.addClass(X.class).addPackage("com.project").createJarFile();
```