KKAppEng should be serializable

[tduffey]

The intent seems to be to store KKAppEng in the user's session but it does not implement java.io.Serializable.  This causes problems when KK is integrated into other applications that are marked distributable and the underlying servlet container (Tomcat, in my case) enforces all session attributes be serializable.  Can KKAppEng be updated to implement java.io.Serializable?