AppNexus: Improved API client unit tests
 * Add base class for AppNexus API client fixtures
   - Includes helpers for setting up mock AppNexus-style HTTP responses
 * Add extensions to create dictionaries from object[]
   - Supports helpers used to improve readability of object building
 * Prevent object disposed/consumed exceptions by loading HTTP request/response message content into buffer
AppNexus: Add report request smoke tests