big update on CV

DATABASE:
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New field 'dom_visible' in table `domain`.
New field 'usr_picture' in table `user`.

SCRIPTS:
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-"ajax_domain.php" : The class "ajax_domain" no longer exists. All its
methods have been moved into the class "domain".
- "ajax_field.php" : The class "ajax_field" will soon know the same fate
as "ajax_domain".
- "index.php" : I added a global field. It will tell the web site to
load the appropriate css/js script (if it exists).
- "models/domain.php", "models/field.php" : Classes "domain" and "field"
have been (almost) completed, I still need to check few things.
- "models/user.php" adding of the methods related to the user's picture.

VIEWS:
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- "views/cv/cv.php" : the cv is modifiable when connected as
administrator. GUI improvement. Actually, there still is a freakin' load
of things to do on the CV, but the hardest part has been done.
- "views/cv/menu.php" : the side-menu doesn't show hidden domain
anymore.

NOTE:
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Because I'm seriously considering adding a blog part into my website,
I'll might have (well... lets be honest...) I'll have to change the
configuration of the database. So, you might expect few changements for
the next commit.