huge piece of code to abstract the notion of Trombino ...

huge piece of code to abstract the notion of Trombino ...
Closes FS#135

The classe XOrgPlugin has been invented to provide some support for big plugins that we want everywhere (like a trombi)
and that are \$_GET driven. The class is made only to manage the $_GET args atm

Note that one restriction (current) is that for a given instance of the class, the plugin cannot been used more that once
(some prefix mechanism should been implemented, but since the need is not here, and that it complicates the code a lot ... not done atm