Some fixes:
- Remove presh zip file after it is downloaded to prevent using
an outdated version
- presh commands are run as the user and group owning the prestashop
installation directory
- Apache virtual host configuration now includes an 'AllowOverride All' entry
because its presence depends on the version of Apache in use. Also, this is
needed when using 'Friendly URLs', which implies URL rewriting rules
through the '.htaccess' file of the Prestashop installation