Change "Smoothen Video" to "Smoothen Edges"

[yani]

The only thing the "smoothen video" functionality does is to smoothen the edges. Changing all references to say "edges" instead of just "video" would make it much clearer.

We could keep the -vidsmooth startup parameter as a legacy fallback, although using a .cfg configuration option would probably be preferred anyways.

[yani]

This has already been renamed to "Smoothen edges" in the Qt Launcher.

[Loobinex]

I'm not planning on updating the old launcher for this.

[yani]

I'm not planning on updating the old launcher for this.

I mean in the code and possible future config option name.