Chatterino2: Seperate "Hide input box when empty" setting for /mentions and /whispers

[cineafx]

It is rarely needed to type in the /mentions and /whispers split (except maybe replying to whispers).
I know you can just disable it for all input boxes but some people like having the empty input box in _normal_ chats.
Quite a few people have /mentions as a seperate split in their chats.

[fourtf]

There will not be a setting for this.

I can see the input being disabled by default for the /mentions tab tho.

[fourtf]

This issue is out of scope of the Chatterino project.