Policy Plus - Show the last sources

Since it's possible that people might not remember what policy sources they were editing last time, and given that Policy Plus now remembers the last policy source (which is almost always the convenient thing to do), it's important for people to be able to see what they're currently editing. Therefore, I added a bit of code to the startup routine that sets up the "Open Policy Resources" dialog to be in a state that would produce the last policy loaders.