V2 API using Pecan and WSME

This change removes the v1 API completely and adds v2 using the Pecan framework
and WSME for (de)serialization.

Also add a small hack where we subclass RestController for now to support PATCH

blueprint v2-pecan

* Not added (Needs be determined)
  Invoice Lines
* Added resources
  Currency
  Language
  InvoiceStates
  PGProvider

  Merchant
    Customer
        PaymentMethods
    PaymentGatewayConfiguration
    Plan
    Product
    Subscription
    Invoice
    Usage

Change-Id: I3d252b05d5d49664e3038fa0b1fa8a6e210d03cd