A proposal to solve the index_static assets precompile issue

# Problem

I got 2 error email from production this morning, I guess you were trying to deploy the `index_static` feature.

Using different layout and only include some css does not work with assets precompile, it's solvable but I don't see it that valuable.

# Solution

So this pull request is just a proposal, feel free to tell me how you feel about it.
I just moved the `index_static` to a "normal" view and use controller + action name on html body as css class to specify the :scope".

This way we can use the power of assets pipeline, and no need to maintain another layout, which I think is handy for developers.