AppNexus: Fix campaign exporter placement targeting
 * Fix method used to get placement targeting
 * Various test helper Linq refactoring to improve debuggability
 * Add wait to DeleteLineItem activity test (deletes not always immediate)
DAL: Fix saving of stream BlobEntities
 * Reads all text and serializes as string
 * Only works for streams containing text

Note: Need to find a way to take advantage of the benefits of directly uploading a stream to a blob