deleting customer apps is now a POST and not a GET, requiring user ocnfirmation.
fix to CustomerController security issues:
  - uses antiforgery token for create/edit
  - edits for unauthorized/nonexisting customer no longer creates a new customer
  - only vendor and system admins can create customers
have a passing test for creating/editing/removing domain licenses manually
-> some fixes were needed in how the license dates were passed as form fields
simplifying DomainLicenseController's models
DomainLicenseController will now only edit/remove domain licenses the user has access to
DomainLicenseController.Remove checks if the sku allows for the domain license to be deleted
Its also no longer a GET request.