[REQUEST] Whitelist publishers and show only them

[gurnarok]

My collection only has a specific publisher books and it would be great to have inverted filtering, instead of using IGNORE_PUBLISHER, there could be value for SHOW_PUBLISHER, that would ignore other publishers and only show the publishers that have SHOW_PUBLISHER tag.

Tried to look at the source code, but my python-fu is crappy and can't get my head around it, so I can't implement it myself.