Bug 1074622 - [Stingray] Scaffold the TV browser

* Clone apps/browser to tv_apps/browser.
* Restructure HTML structure and style for TV browser UI.
* Draft modules for TV browser.
In the original browser app the 'hidden' class name is defined in css files like:
#some-id.hidden {
  display: none;
}

Definitions like this are all over the original style sheets. Using these kind of style definition could be overwritten if some other developer adds some thing like
#some-id.shine {
  display: block;
}
... after the line of #some-id.hidden .

Why change it to 'is-hidden':
1. the unexpected error describe earlier should be prevented, the class definition is also changed to 'display: none !important;', 
2. reduce style sheet lines,
3. since the 'hidden' class is used universally to hide elements, it is proper to use one class definition in one place to prevent the effort of adding/removing it for every element that needs it

'is-hidden' is just a stateful naming pattern borrowed from the concept of SMASS. If in gaia we use 'hidden' in common then I'll change it back.