scripts: Follow symbolic links when adding a new site

When the skeleton dir is a symbolic link, the content of the link will
be copied and not the link itself. Copying the link itself breaks the
skeleton when the site is initialized.
scripts: Remove git repos when a new site is added

If the skeleton is managed in a git repo itself this information should
not leak into a new site.
core: add Steffen Hanikel to contributors file
mod_menu: Hide the removal option when a menu item is protected