Frames can no longer be serialized because a new field: "private SoftReference
softThis" was added to the class, but SoftReferences are not Serializable.
Attempting to serialize a Frame now throws an Exception.

Since "softThis" should be reset when the Frame is deserialized anyways, this
field should be made transient.

In addition, Frame.readObject() should be modified to give "softThis" a valid
value before calling addToFrameList(). Otherwise, null will be inserted into
the list, causing a NullPointerException when getFrames() is called.