Change $wgSlackFromName default to $wgSitename

[labster]

Could you make the default value for $wgSlackFromName =$wgSitename? We're probably going to install it on the @miraheze wiki farm, and that would make default config a little easier. And it seems like a sane enough value.

I'm the security reviewer over at Miraheze, and it looks like a pretty good extension to me. Thanks.

[kulttuuri]

Great idea! Let me change that :) 👍

[kulttuuri]

Done and committed!