A few tweaks to the forum design

I’ve added a few logos and icons to the new forum. At least now people will have a better idea of which site they are visiting.

The intention is still to create a darker layout to match the main site in the long term. But that may take some time and is not a high priority for me compared to other projects. Also @UrbanReflex was looking into the colour scheme too I believe, so the design will be implemented by whichever one us gets around to it first.