Make favicon board-wide and not theme-specific (with backward compat) - fixes #2573
Make favicon board-wide and not theme-specific (with backward compat) - fixes #2573

emanuele45/Dialogo,Spuds/Elkarte,emanuele45/Dialogo,StealthWombat/How-to-fork-an-Elk,Spuds/Elkarte,nwsw/Elkarte,elkarte/Elkarte,elkarte/Elkarte,StealthWombat/How-to-fork-an-Elk,interlab/Elkarte,StealthWombat/How-to-fork-an-Elk,emanuele45/Dialogo,StealthWombat/How-to-fork-an-Elk,elkarte/Elkarte,interlab/Elkarte,nwsw/Elkarte,interlab/Elkarte,Spuds/Elkarte,nwsw/Elkarte