Refactor "class Serializable"

[dsuponitskiy]

1. In Serializable: implement virtual SerializedObjectName() to return the correct type name of any object derived from Serializable and remove all other implementations of SerializedObjectName().
2. In Serializable: implement static SerializedVersion() and remove all other implementations of SerializedVersion()
3. Make sure that:

• all classes having save() and load() implemented are derived from Serializable
• the version number is checked in every load() function (as some classes miss a. or b. or both of them)