Add Video search without a parent account/channel

For instance, search for the most viewed video on the whole YouTube running:

```ruby
videos = Yt::Collections::Videos.new
videos.where(order: 'viewCount').first.title #=>  "PSY - GANGNAM STYLE"
```
Merge pull request #72 from Fullscreen/yt-video-where

Add Video search without a parent account/channel