Card gem or the Card/Deck Split

Again, just for discussion for now.

I've looked a little at how rails does the many projects in one repo and tried to do something similar here.  My thinking now is that if we get this split right, then everything needed for the platform is in the card gem and the wagn (soon to be decko) gem is what makes it case 1, a web application that uses the card engine.

It took me a while, but I got it to load and run the few specs left behind in the wagn part.  Seems like the mods should be split, but many of them are core.  Please add your comments about what is core and what is not.  I'm thinking that things like accounts has be be with the deck as authentication is a site issue.  Default is a plain card, and then we are using card_ids as the creator/updater.  Question for all is how we want to connect to an external user model, do we always want to have a card with a card_id that is associated with the external mode?  Is that just another instance of an external model bound to a deck via a standard way of doing that?  My plan was to add card_id to the external table (making it belong to a card and the card will have_one of the external model).

The part I haven't figured out/finalized is the way the top level objects should work.  Initially I thought (wrongly) that the Engine (Card::Engine < Rails::Engine) needed to be part of the Wagn::Application < Rails::Application object, but there just isn't a way to have one object fill both roles.  And this split implies that the application will always have very simple routes that mount the Card::Engine thing, and the same thing in the platform use, but you'd have all your application's initial routes.  We may also want to split out some of the legacy routes to the application and leave only the platform standard stuff in Card::Engine routes.
This was a narrower comment.  I just meant that I would want to be particularly hesitant to included low-level caching changes in a large PR like this, because caching bugs are notoriously difficult to root out.  I don't object to these particular caching changes but would urge to keep them separate and not get into the slippery slope of tweaking things that are only tangentially related to the issue at hand.

I'm not insisting on any particular change, just asking that we try to get this stuff merged in before going much further.  Most of what you've done seems quite mergeable, so it would be a waste to turn this into a more highly experimental branch.