utf-8 compatibility for web UI

webadmin/EN/about.html

webadmin/EN/add_app_confirm_template.html

webadmin/EN/app_add_template.html

webadmin/EN/app_installing.html

webadmin/EN/app_remove.html

webadmin/EN/app_remove_scheduled.html

webadmin/EN/app_scheduled.html

webadmin/EN/app_template.html

webadmin/EN/apps_add_template.html

webadmin/EN/apps_template.html

webadmin/EN/backup.html

webadmin/EN/backup_complete.html

webadmin/EN/backup_confirm.html

webadmin/EN/backup_failed.html

webadmin/EN/backup_password.html

webadmin/EN/backup_progress_template.html

webadmin/EN/blocking_template.html

webadmin/EN/bridges_template.html

webadmin/EN/dynamicdns_template.html

webadmin/EN/factory_reset_confirm.html