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

I want to write it ONCE but make sure future writes does't get notifiably delayed by  ~500ms, bacause the API is requesting the port via corba name service again.

A high timeout prevents lag in remote control, also when the port is not constantly written. I can imagine situation where a remote control via this html element has gaps between commands higer than 30s but not 5 minutes (this timeout is ONLY for the motion2d ui element, not for the values from the taskmanager). But the Timeout applies to whatever is used first though