Support of the webm and webp format

[perfektionix]

As the newer multimedia container formats webm and webp are gaining in importance, and the restriction is probably only superficial (both can be rendered by renaming them to *.mov or *.png), it would be nice if these formats were officially supported.

[aspettl]

I checked, it is unfortunately not that simple:

• For webp, on my system it does actually work when I add the file extension in WordsLive. But according to WPF documentation (WPF is used to load the image) webp is not on the list of supported file types. Probably it just works because something else is available on the system - maybe even provided by Microsoft or Windows itself, but I don't know in which cases that is available.
• For webm video files, it does not work for me to just add the file extension. The renaming trick works, but loading it with the webm extension does not. As as for webp, webm is not on the list of supported files by WPF.