Buffered Ports 

Re-issue of pull request https://github.com/planthaber/rock-webapp/pull/11 against master
The code doesn't keep thrack of the deadline, it updated the last time the port was written to.

The timeout is only evaluated because it might be changed on user request:

* first call sets a low timeout of 30s ->lifetime is 30s
* second call setd a higer timeout of 200s -> lifetime_s needs to be updated to updated to the higer value
* another call used a low timeout of 30s -> the timeout stays on the higer value

In line 54, the timestamp of the last usage is updated,