Merge pull request #527 from protherj/gw-prov-dialog

Made the authorize.net provider dialog work
demo update
Merge pull request #528 from rustyswayne/1.0.1

demo update
Housekeeping
Merge pull request #529 from rustyswayne/1.0.1

Housekeeping
Updated Merchello version
Updates GatewayProviderApiController to include Put method for GatewayProvider dialog displays.  Wires up Angular service.
Merge pull request #530 from rustyswayne/1.0.1

Adds a GatewayProviderApiController Put method for dialog saves.
Exposed a bunch of IInvoice and IPayment extension methods to allow front end designers to more easily integrate Plugin payment providers.
Updated Umbraco dependencies to 7.1.1
Replaced hard referenced Merchello dependencies with Merchello.Core NuGet reference in AuthorizeNet provider. Patched AuthorizeNet integration tests.
Merge pull request #531 from rustyswayne/1.0.1

Bunch of stuff relating to payment providers
refactored Payment settings page / controller / models to allow for multiple providers