Implemented new tabs visual design

- The tabs bar is not hidden any more.
- Some UI tweaks are required for the case of 1 tab.

![screen shot 2014-04-28 at 4 01 27 pm](https://cloud.githubusercontent.com/assets/332168/2824011/2afab182-cf29-11e3-8879-57e53839546a.png)

#1548

review: @devoncarew