Accept some setting to run in a path

[fernandocollova]

What happens?

When running behind a proxy, (in my case, Apache adding SSL to the connection) the app doesn't honor the X suite of headers, and also doens't have any settings so one can run it in /playmaker for example.

What should happen?

The app could have the xheaders argument set to True when calling tornado.httpserver.HTTPServer and some way, maybe an env var, to set the app to "tune" the urls to other dict.

How to reproduce?

Basically, try to access the app behind any proxy using a path different from /. For example, this apache ProxyPass settings stops the app from loading any static files.

<Location "/playmaker">
ProxyPass "http://127.0.0.1:5000"
ProxyPassReverse "http://127.0.0.1:5000"
Require ip 192.168.1.0/24

Some meta

I have transmission, nextcloud, and other apps running in the same host, and it just feels wrong to have this in "/" when I could have it properly configured in it's onw path. Also, most of those services I use have by default a leading path, so maybe this app can have it as well? Would you accept a pull request for that or some other way (as an env var) to set that path? Or maybe both, a default that's used if no env is provided?

The thing I again just can help is the JS part, as I don't know any of that. But I guess if the path is hard-coded it shouldn't be too difficult to add.