feat tabs: add color themes

Tabs colors can be customized now : indicator color, active bar color and ripple color.

![capture d ecran 2014-12-01 a 10 12 39](https://cloud.githubusercontent.com/assets/1220284/5243298/a7b9e166-7942-11e4-9a12-4d8018af3291.png)

Same as the other PR, you need to watch the value for change, not set it only once.