Migrate to sinatra/puma from webrick

As I can't do IO#select on sinatra/puma to run it when I have time, I
have to run it on separate thread.
This means Nodes container needs to be thread safe, it now has ghetto
mutex locking, but I probably need to be be more focused what are the
external methods that can be called and wrap those in @mutex.synchronize

Provide also HTML UI not just JSON for ghetto UI to people who don't want to
integrate