Re-structure and simplify menu layout

This pull request merges all menus together in an effort to simplify the layout and make it less cluttered. It can be previewed live here : http://bitcoinmenu.us.to/en

**The following pages are renamed (redirected) :**

bitcoin-for-press - becomes press and is moved in resources
bitcoin-for-enthusiasts - becomes innovation and gets more visibility.
~~resources - becomes links~~

The new Innovation page could qualify for a complete rewrite focused on explaining the real innovative nature of Bitcoin. Everything that can start with "it is the first time in history.." would fit there. With a few short insights of the potential and impact it could have.

The About page should be replaced (and recycled) by a FAQ in the future.

**Compatibility**

This layout remains compatible with IE6, mobiles and all browsers that were supported.

**Progressive deployment in translations**

This pull request also implement a new _redirects.yml file that allows to interfere with template.rb plugin in order to generate page redirections for selected pages and languages. In such a way that any change in website structure can be deployed progressively in translations without breaking layouts, page urls and sitemap.