Big merge

I know that this PR is quite a big merge...

But I think that it will evolve this cookbook in a good way :)

what I do:
* Add berkshelf / vagrant support
* Add support for Emperor
* Add a LWRP to add a new instance to emperor
* Add a way to install uwsgi via gem (ruby support)

FUTURE: New cookbook structure permit to add a "install via packages".
I'm currently doing some work on launchpad to create a new ppa.
I will do another PR when this job will be done.