app list layout pages (bug 1103294)

The new images assets are still missing but I'm adding them shortly.

![](https://s3.amazonaws.com/f.cl.ly/items/0j0325183c323n112m3V/Image%202014-12-17%20at%204.35.58%20PM.png)

![](https://s3.amazonaws.com/f.cl.ly/items/1V0v1P3d2w1H0P043Q2O/Image%202014-12-17%20at%204.36.41%20PM.png)
```tabs``` is a bit generic, i'd call it like new-pop-tabs.

BUT i'd look into using ```<mkt-tab-control>``` supplied by marketplace-elements. it seems to look the same and follow the style guide. https://github.com/mozilla/marketplace-elements/blob/master/marketplace-elements.js#L222