[ticket/10741] Function to resize textarea elements

New function to automatically resize textarea elements
as user types text

PHPBB3-10741
[ticket/10741] Automatically resize textareas in prosilver and ACP

Automatically resize textareas in prosilver and ACP.

PHPBB3-10741
[ticket/10741] Do not resize textarea.no-auto-resize

Do not auto-resize textareas with class .no-auto-resize

PHPBB3-10741
[ticket/10741] Fix for browser-specific resizing of textarea

Disable browser-specific resizing only after textarea has been resized
Enable browser-specific resizing after script resizing has been reset

PHPBB3-10741