Strong Paramaters

Basic model changes to get drop_ship working in Spree 2.1 with Strong Parameters enabled.

Tested on Spree 2.1.3:
* New/Edit Order & New/Edit Drop Ship order ( I had to add //= require admin/spree_drop_ship to all.js )
* New/Edit/Delete Supplier
* I created orders in both the Admin console & the API
* I logged in as Supplier, works as designed.

Not Working:
* When you login as a Supplier and create a Stock Location, it doesn't associate the Location with the appropriate Supplier.  It looks like this is not a new issue.  I looked at 2.0 and its the same behavior there.
* The edit & delete links on the Supplier index page are still broken.  The links use the slug name like this:

`/admin/suppliers/mysupplier/edit`

But the drop_ship controller won't respond to these.  I changed this links to use ids instead. i.e.:

`/admin/suppliers/10/edit`

This works great.  However i'm not including the change in this PR b/c i figure you want to stick with permalinks.

cheers,
matt