Quick search should use a placeholder

Signed-off-by: emanuele <emanuele45@gmail.com>
And the moderation center add note too

Signed-off-by: emanuele <emanuele45@gmail.com>
Removed the strict_doctype option from theme and source (should be useless nowadays) - fixes #608

Signed-off-by: emanuele <emanuele45@gmail.com>