Option for pedantic mode warnings

[WardBrian]

The Stan compiler can provide additional, "pedantic" warnings which will do things like warn against having multiple priors on the same variable.

These can be noisy (and even downright incorrect, since some are heuristic), so it would make the most sense to have this be an opt-in of some kind. Maybe there's an options pane for the text editor, or maybe we consider making the server connection window a more general "settings" window?