Changes related to external subtitle renderers

The commit messages are rather straightforward. The last thing was something requested by cyberbeing, and is the most controversial of them all. Discussion welcome.

> \<JEEB\> well, the real root of the problem is the whole new madshi's subtitle rendering interface to be honest, I remember then trying to get Lord and nielsm/jfs and others to come up with good ideas to fix its problems, but in the end the only comments were 1) it shouldn't even touch DShow really (as it's trying to be the new CSRI) and 2) We can't do much because the only implementation of the renderer side of things is closed source, and the DShow part is
> \<JEEB\>  already implemented
> \<JEEB\> on the other hand, what cyberbeing now wants is:
> \<JEEB\> 1) if madvr && xysubfilter is registered -> vsfilter doesn't get used
> \<JEEB\> ^ this is what the patch does, more or less
> \<JEEB\> 2) if ISR enabled && xysubfilter is registered -> xysubfilter doesn't get loaded (which is kind of hard becaue the video renderer is supposed to load up all of the renderers into the chain no matter what the graph builder tries to do)

tl;dr:
- Adds GUIDs of VSFilter and XySubFilter to moreuuids.h
- Uses the VSFilter define in AppSettings
- Blocks VSFilter in the currently only case where XySubFilter would get used.