Several updates/fixes

Layout:
- added class .inbl (display: inline-block)
- added class .relative (position: relative)
- renamed .margesauto => .center
- Added width and max-width sections in em/px

Global structure:
- element are no more targeted by ids

Forms :
- fix typo inputs
- added class .label (field texts)

Everywhere
- added/enhanced lots of comments