Where to store the interpreter data

Well, currently data for the interpreter is stored at a preference store.

I made up a InterpreterPreferencesPage and just convert from the interpreter data to its serialized form and vice-versa, using the preference store for it (you can even see a huge nonsense string if you go to help->about->configuration details -- that's its serialized string).

This is good so far, but if later more data is stored here, we will need to get somewhere else to store it, probably using the plugin instance to get it (apparently with 'getStateLocation') - according to this article: http://www.awprofessional.com/articles/article.asp?p=370626&seqNum=9&rl=1