Add server side rendering

[bitspittle]

https://www.google.com/search?q=server+side+rendering

We are already running kobweb on the server - it's mostly being used to serve static files and respond to server API requests right now. The next natural extension is to figure out server side rendering, where the server could be configured to deliver custom pages per user.

This bug is useless if #113 isn't solved first.