Add another todo.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Make `weechat-hidden-text-hidden' static.

The dynamic hiding of text, enabled with `weechat-toggle-hidden'
showed really abysmal performance, making Emacs almost unusable with
'big' weechat buffers (>1000 lines).

Dropping features isn't nice, but until Emacs gets a *big* boost for
the invisible text-property we should remove this feature.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>