keep references of ports and writers and remove them only after a timeout

The GC can collect them any time after the timeout.

Hopefully solves this Issue https://github.com/planthaber/rock-webapp/issues/2

I opted for two things:

1. The timeout parameter to be a GET param (inside the url ../port/write?timeout=30).
2. Instead of adding callbacks for each writer, there is a single callback who cleans all references to writers where the timeout time has passed (like a timeout based garbage collector). Still, there are the other options: callback for each, set callback time to next timeout

you mentioned once that the first timeout "wins". Shouldn't you simply pass the timeout parameter to this call in order to be able to "update" the timeout ?