Allow remote network access

By default the flask web-server would listen only on address 127.0.0.1, which makes it inaccessible from the network. Unfortunately we have not tested this before :'(

So lets listen on all interfaces. And while being at we also change the default port from 5000 to 8080, which is commonly used for alternate http services.

And to make live on the other end of the line easier also allow POST as method besides PUT to assign a new value.