Better Error Messaging when Starting

[fireproofsocks]

It's gotta be cleaner, e.g. have a post-form on the error page.

The friendly_urls, moxycart.domain, apikey will trigger the error. The trick is that the error page needs to look differently when it's inside a store-container tab vs. when it's on one of the Moxycart CMP.

Maybe we can display the full version via the ProductContainer controller?

Gotta move the IndexManagerController::_checkSettings() to a model class.