Edits and adaptation for the new Class Contents

Note: Changed the query-string from 'prod_id=' to 'id='.

* controllers/_database.php : Created the new class Contents and the
relative functions.
* controllers/_init.php : initialized Contents.
* controllers/_templating.php : Edited the list() function to get
action= as option.
* index.php : Adaptation and edits for the new Class.
* views/admin.index.php : Removed it's contents and moved to
admin.products.php.
* views/css* : Minimal edits and fixes.
* views/view.cart.php : Minimal edits.
* views/view.details.php : Added an 'Edit Product' link.
* views/view.index.php : Made the index to fetch contents from the db.
* views/view.products.php : Minimal edits.
* views/view.sidebar.php : Minimal edits. Added 'Manage contents' link.
* controllers/contents.php : First commit.
* views/admin.contents.php : First commit.
* views/admin.products.php : The moved content from admin.index.php.
* views/view.content.php : First commit.

Deleted: controllers/cart.php and moved it's contents to products.php.