Allow protocol agnostic urls

When embeding a link such as

```html
<a href="//www.youtube.com/watch?v=RVmY2lQ4DHE" embed-video></a>
```

The plugin fails to embed the video, because it is looking for a protocol to reconstruct the iframe src embed. 

Sometimes we need to use links like this for example if our development environment is on http, and our production environment is on https. We generally use protocol agnostic URLs to avoid secure to non-secure browser warnings and restrictions. 


Also includes a fix for `grunt bower-install` to identify the correct file for injection.