Re-structure design and layout

This pull request can be previewed live here : http://bitcoinhome.zapto.org/en/

**Most important changes in this pull requests:**
- Right buttons are removed and merged with the menus.
- A new introductive home page with WeUseCoins video.
- A new "Getting started" page with links to external merchants and exchanges directories.
- A re-design for "Community", "Resources" and "Download" pages.
- New links to bitcoinmining.com, coindesk, thegenesisblock, usebitcoins.info, howtobuybitcoins.info and letstalkbitcoin
- Titles and pages summary are consistent and centered.

**This work has been done with the following goals in mind:**
- Provide a better introduction to Bitcoin.
- Bring users to inform themselves before anything.
- Link more contextual useful resources with an acceptable level of warnings.
- Offer a more consistent, sober and readable layout.

**Tested browsers:**
IE 6+
FF 3+
OP 10+
SA 3+
CH --
Android 2.3

**Future improvements:**
I planned to replace the About page by a FAQ later, and rewrite the Innovation page.

**Migration:**
Deprecated transitional HTML and CSS code is isolated in such a way that previous layouts will remain online for translations until they have been updated, after what it will be possible to drop this code.

**Yes, it's a lot of changes:**
Sorry for the huge pull request, doing these changes individually would produce an inconsistent result. I have already pushed many non-controversial changes to reduce the size of this pull requests as much as possible.