Fix #12 WebsitesController#update mass-assignment

Add missing attributes to mass assignment whitelist
Should be moved to strong_parameters later
Add dibs_merchant_id and dibs_hmac_key to websites
Add dibs_hmac gem and DibsIntegration class

This model gathers all info we need to integrate with DIBS Payment
Window
Extend OrdersController#create to handle DIBS

Remove payment_type "credit_card",
instead use "dibs" or "paypal"
Temporarily set thank_you_url as callback
Merge pull request #13 from standout/dibs-integration

Dibs integration