GStreamer Video - Move code to new class instead of updating existing class

[jmgasper]

Problem

We want this new GStreamer code to be next to the existing pxVideo / AAMP implementation. We shouldn't be changing pxVideo.h and pxVideo.cpp

We need to be adding new classes that do the same thing, but without the AAMP reference. It's confusing because the client added this pxVideo class without thinking about how it's going to conflict with our work, but we need to work around it. The goal is to support AAMP and the GStreamer implementation side-by-side. It's understood that this will cause some redundancy issues, but that's something we'll just have to live with.

Fixes

Let's do the following:

1. Revert the changes to pxVideo.cpp and pxVideo.h from the previous challenge
2. Add new pxHtmlVideo.cpp and pxHtmlVideo.h files with the required GStreamer and other code.