Add feature to show/hide bits of a guide based on preferences

Add support for embedded CSS classes that allow hiding segments of a guide based on build systems. Embed these selections in a cookie so that preferences are carried across various guides.
This is a *lot* of event handlers.  There just has to be a way to simplify it using jquery event delegation, perhaps coupled with a data attribute on each triggering node to specify which type it should reveal.

Also, in general, any event handlers that are added in `ready` should be removed in `destroy`.  I just did a couple quick checks and we're not doing that everywhere (d'oh!), but even so, it's the right thing to do.