Enabled tags on the forum

I enabled tags on the forum per @vsund’s request on slack.

Can always turn them off if they don’t work. Let me know what you think.

The default setting for trust level to create tags was 3 - normal users are 2 - since I don’t think we really have any users who have made it to trust level 3 yet, I reduced it to 2. We can adjust it later if we have tag spam problems etc.

Thanks @vsund for getting in touch with me about the problem!