Allow forcing host in config

[gennyble]

I've many a time forgotten &forceraw when testing and was confused why it wasn't showing new changes.

[gennyble]

I have textual setup behind a reverse proxy via Nginx. I suspect this is how a lot of people will have it configured.

• [ ] Give an example Nginx config
• [x] Allowing setting a Host to use in the config as opposed to using the header #3
• [x] Allow forcing scheme. This is useful when Nginx reverse proxying because textual sees the connection as http and sets the link to http, forcing a redirect when getting the image in the browser. This causes the browser to say some parts of the page are insecure.

[gennyble]

Closing without the Nginx config 83ad995