Make FieldValidator and Resources constructors private. This classes
should not be instantiated. Fixed related consumer classes.
Refactoring: removed unused code and imports. Fixed warnings.
Refactoring: renamed catalogue package to dialog. Renamed related
clases.
Refactoring: migrated dialog gui classes from jframe to jdialog, and move them to dialog package.
Refactoring: renamed and rearranged panels packages and clases.
Refactoring: renamed and rearranged dialog packages and classes.
Refactoring: removed unused import from Author entity.
Refactoring: reformatted code. Fixed indentation.