Adapting Galanthis : part 3

Adapating
- Deleted script_dessins.js and script_installations.js : replaced by
script_form_image.js to be more adapted to the user's needs (a sole
category is enough)
- Deleted post_file_dessins.php and post_file_installations.php :
replaced by post_file_image.php to be more adapted to the user's needs
(a sole category is enough)
- form2.php edited for the same reason
- edit_position.php edited for the same reason
- update_contact.php, index.php, new_texte.php, update_link.php,
add_text.php and update_text.php got their HTML header corrected (css
changed, title changed)
- New_texte.php renamed in new_text.php
- delete.php upgraded and adapted, it now deletes the files on the
server (!NEED TO BE TESTED ON BOTH LOCAL AND DISTANT SERVER!)