gui2/taddon_description: Let the description area grow horizontally

Let it grow to fill the space available when it's greater than the
description box's requested size (e.g. for very short descriptions).
gui2/tchat_log: Use 'description' scroll_label type for the log
gui2/tchat_log: Let the log scroll_label grow horizontally
gui2/tchat_log: Hack to set a minimum cell size to 200x250

Because this window many contain a lot of text in both directions,
having it change size dynamically every time the log page is switched or
a new text filter is entered can be extremely annoying for the player.

Setting the scroll_label's parent (now ancestor) cell's minimum size to
something that isn't 0x0 mitigates the issue to some extent. Better than
nothing, I guess.

(Tested with a screen resolution of 800x480.)