Offer a lightweight version without the web app

[wrobelda]

The current docker container uses about 700MiB of memory while in use, mostly because of node.js app. The app itself, however, is not something most use a lot, so it would be nice if you offered an alternative docker image with bare tftp setup only.

[wrobelda]

Actually, my bad, memory usage is much lower, sitting at ~70 MiB in fact. Still, for security purposes, I am not even exposing the 3000 port of the web app, so a lightweight version, or even a mere env variable that would effectively disable the webapp couldn't hurt.