[RFC] VideoCommon: Datareader

This branch tries to reduce the global state within our Fifo - OpcodeDecoder - VertexLoader - VertexManager queue. All globals between this stages are removed and replaced by function arguments.
Also a new DataReader helper class was created for easier parsing of binary streams
Get/Set here is a bit confusing as this is a vertexloader function which is queued to "get" the destination buffer. But as we can't return anything, it's stored in the global variable bufferPos.

And I think we can improve this by removing this kind of bbox implementation :D In fact, I want to rewrite the vertex loader in additional steps and I won't care about the bbox at all. So it will be a ogl4 only feature - or als od3d11 is someone will implement it :/