Unit-09: Add CopyCharacters.java

Package: com.practicaljava.unit_09.iostreams
Unit-09: Improve WriteBytesIntoFile.java

Add a FileNotFoundException catch and its handling.
Unit-09: Add test classes Employee and Manager

Package: com.practicaljava.unit_09.serialization
Unit-09: Modify Employee hierarchy for serialization

Package: com.practicaljava.unit_09.serialization
Unit-09: Add TestWriteAndReadObjects.java
Unit-09: Add "serialVersionUID" fields to Employee and Manager