Slight variance on clip position when loading save on separate system

[dfaker]

Reported by @30secstf

I do the editing and the encoding on two different systems and while subclips loads more or less fine (sometimes they are slighly shifted by few frames, it is noticeable because of the scene change and I have to manually shift the subclip) but filters aren't loaded at all.

Also it would be useful if WebmGenerator would search for the video source in the same folder as the .webgproj file first, regardless of the path.