[ticket/12166] Add template events to quickreply_editor.html.

Add template event pair - quickreply_editor_message_before
and quickreply_editor_message_before to
quickreply_editor.html for both of prosilver and subsilver2 styles.
This allows extensions to modify quick reply
postform. For example, to add BBCode buttons and/or smilies
and so on.

PHPBB3-12166