Add backend form error messages

Currently global form errors (extra fields, csrf, etc) are not displayed in backend.
This commit adds one to discuss if this is the desired approach. (will do all if OK).
Fix Shipping Method Calculator form prototype handling

Currently, switching the calculator field in the ShippingMethodType embeds calculator config prototypes under __name__ key, which causes the form to not validate. This commit makes the following changes:
 * use the proper field name (configuration)
 * skip embedding forms for calculators that don't support configuration (currently results in empty text field being embedded)
Merge pull request #1 from Sylius/master

Merge with current version
gitignore
Fixed discount promotion calcutaion
Revert "gitignore"

This reverts commit 46532fd7902bc74a831b17ae2f724650befac864.
Add global form errors to backend forms
Adding global form errors to some Frontend forms
Spec and test fix for percent discount
Behat tests
My account / addresses :
 - improving Behat tests
 - delete cascade on table sylius_user_address
 - listener to directly add the address to the current user (when an address is created) and to directly unset billing and shipping to the user (when an address is deleted)
 - main featurees
My account / addresses :
 - improving routes
 - improving templates
 - finishing "set as default address" features
My account / addresses :
 - translations
My account / addresses :
 - fixing Behat tests
 - now test user is sylius@example.com (like in the fixtures) and his password is sylius
My account / addresses :
 - minor fixes
My account / addresses :
 - isolating routes
My account / addresses :
 - Behat tests
 - fixing addresses test code
My account / addresses :
 - fixing translations
My account / addresses :
 - extending ResourceController
 - using custom action for create instead of using Listener
My account / orders :
 - fixing routes after rebase