Add tab for videos (and call it videos)

[Popolechien]

There are too many TED videos at the moment and this is not going to improve (hopefully it will not as we want to grow available content). But with 606 zim files available in English, this creates poor UX when selecting content.

I suggest we create a Video (or TED) tab on the imager. While not ideal, that would allow to separate grain from chaff. Since categorization is an issue, in the short term I'd suggest populating with TED-labeled videos (the library already allows to separate those).

Another problem (maybe) is what happens when a language has no TED/videos. There should be a basic message None available in your language maybe'