Greatly reduce number of drawn routes on Spree::Core::Engine

By prepending routes as we were doing before, Rails was not checking to see if the routes already existed and therefore drew over 1,000 routes for Spree and it's things. This, of course, would take time and RAM.

By calling draw, Rails checks and therefore doesn't draw the routes if they're already there.

Thanks to @parndt for pointing this out.