Add support for OpenRTB protocol and endpoint (#2102)

* Update to use OpenRTB protocol and endpoint

* Refactor request and response handlers

* Handle adding bids in core response handler

* Update openrtb endpoint response interpreter

* Refactor variable names, update comments, extract cookie sync to core handler

* Update openrtb bid response fields

* Match bid ids

* Update based on review feedback

* Move legacy-specific video code to legcy spec

* Add video support to OpenRTB spec

* Add digiTrust, app, device to request

* Default to banner if mediaTypes not defined

* Allow single or double banner.sizes array