added buffered port readers

pull request for port writers to the add_syskit_2 branch (new folder structure).

replaces https://github.com/planthaber/rock-webapp/pull/6 for the old folder structure


open issues:

* use Websocket communication to know when the buffered port is not needed anymore
* let the EM send timeout events (no periodig cleanup) 
 * solved by websocket?
 * provide both APIs