Move icon.

--HG--
rename : scheduler_error_mailer/static/src/img/icon.png => scheduler_error_mailer/static/description/icon.png
Fix some formatting.
Only admin can send emails here.
Don't pollute other models just for testing this one.

--HG--
extra : amend_source : d3da15fc7b28f738dbef0e7a60044b4f71056b06
New translation template.