add keybinding for `weechat-toggle-hidden'

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>
Recenter window when it's necessary

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

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