serve dojo_theme/static directly via nginx

[zardus]

This (marginally?) reduces the load on our ctfd workers by serving (some) static content directly via nginx. Some caveats:

• CTFd does automatic fallback to the built-in files for stuff dojo_theme doesn't override. Because of this, I still have to forward the request onwards to ctfd (to avoid mounting ctfd into the nginx container somehow), so this only handles probably less than half of the static requests.
• I have no idea what the security implications are of this. I think it's fine, but not completely sure.