fix video endslate icon

- Change video endslate icon from dark to white

![image](https://cloud.githubusercontent.com/assets/960919/4370905/9da1e7dc-430f-11e4-9f72-2482893e06b6.png)

![image](https://cloud.githubusercontent.com/assets/960919/4370907/ac9ba35e-430f-11e4-8142-edfcecf82b5a.png)

We should try to avoid nesting.

This will create:
`.end-slate.items--video .item__title:before' <- which have massive specificity. Only way how to reuse this is to create another big selector/class.

We already have:
'.item--video .item__title:before,
 .linkslist__item--video .linkslist__action:before' + white icon if it's nested under '.container--dark-background'

So there is no reusability of this because it's so dependant on HTML structure.

It would be much nicer to see something like this:

`.video-icon--white'
`.video-icon--black'
`.icon--small'

Etc. You can see the pattern. And then the icon wouldn't be dependant on HTML structure but can be easily reused across the page(s).