hide menu chat setting

[cg]

(a) it's ugly af and utterly redundant for anyone who uses rightpane
(b) there's currently no way to actually fully hide chat anymore, which is a pretty important feature

low priority but also probably about 2.5 lines of code

[serprex]

NB there's /mute which is muteall when given without argument

[serprex]

https://github.com/serprex/openEtG/commit/6a782dfc25eea1792a7fdbb57cddccbfd6d2d396