Added support for importing XLS (Excel) files.

Added support for importing XLS (Excel) files.
Download available:
-Products
- Store categories
- Shop collections
- Manufacturers Store
- Articles
- Bases of e-mail addresses
- Forwarding list.

Added support for importing XLS (Excel) files.

Added the "Attachment level" parameter to the main menu items
Added the ability to set a tax with automatic recalculation of the final cost.
Added option to configure the display of the category list on the site