Switch the Customisation Database BBCode Help field from Text to Textarea

The phpBB.com Customisation Database has not followed the improvement that extended the BBCode Help from 1 line only to a Textarea/Memo field of 3000chr in phpBB 3.3.5...

https://tracker.phpbb.com/browse/PHPBB3-16804

https://github.com/phpbb/phpbb/pull/6254

If works fine in phpBB 3.3.5+...

 
But we can still submit only 1 line help in the Customisation Database...

The Customisation Database "Help Line" field should then be renamed to remove the word "Line", like "BBCode Help" and the field switched from a Text field to a Textarea with a limit of 3000chr.