Removed HTML from admin_warning template and replaced with calls to editable template show_error

Signed-off-by: Antony Derham <antonyderham@gmail.com>
Replaced string 'Warning' with a  language variable

Signed-off-by: Antony Derham <antonyderham@gmail.com>
Merge pull request #1552 from Ant59/remove-subs-html

Replaced HTML in template 'admin_warning' from Subs.php