fixes #2345 create piwigo standard pages

create new theme standard pages with tpl, css, js and images
update backend to handle pages
add config use_standard_pages
on update set config to false, on install set config to true
add standard pages to no be ingored in git

admin/configuration.php

@@ -50,6 +50,7 @@ $main_checkboxes = array(
     'show_mobile_app_banner_in_gallery',
     'show_mobile_app_banner_in_admin',
     'upload_detect_duplicate',
+    'use_standard_pages',
    );
 
 $sizes_checkboxes = array(