VAST 2.0 Support — From what I can tell you only supported VAST 1.x

I've modified mostly `DVVideoAdServingTemplate+Parsing.m` to be able to parse both VAST 1.x as well as 2.0 XMLs. I tested with a VAST XML I have from a Client with an Inline ad in both VAST 1.x and 2.0 variant.

I also have to work on Wrapper for VAST 1.x and 2.0 — You seem to have thought about supporting it (given there is `DVWrapperVideoAd` — did you get anything done?