Moving social network meta description logic from the template header to a bunch of helpers.

Refactors the image fetching to mutualize resources.
Refactoring the date translation helper.
New theme coming.

For some reasons (lazyness being one of them), this theme was not built to be shared.

- My pic by default
- French

Feel free to adapt anyway.
Updates pages rendering.
Fixes the note display.
Adds h1 for notes.
Fixes related posts.