refresh app detail page pt.1, app tile (bug 1103201)

Mock: https://www.dropbox.com/sh/7v0lv4rm70139o7/AACc_XBUl2TC5ALeR9ksdunQa

- button color definitions now using the common colors.styl palette
- preview CSS moved to diff file
- detail CSS now in css/detail, split off into different portions of the detail page
- copy for the app notices shortened
- some CSS selectors made less specific (e.g., remove ```.listing``` from detail page, have preview trays use ```.tray``` over ```.mkt-tile .tray```

![screen shot 2014-12-26 at 6 32 57 am](https://cloud.githubusercontent.com/assets/674727/5557974/5c16a10a-8cc9-11e4-8185-ab36cf3e320f.png)

![screen shot 2014-12-26 at 6 34 51 am](https://cloud.githubusercontent.com/assets/674727/5557975/5f737472-8cc9-11e4-8a90-98cc4b717d9d.png)