* add a lumiera_interface_version() function for runtime type and version
checking of interfaces
* the 'lumieraorg__plugin' interface is now private
* add a macro to construct a interface instance name string
There where some bugs slipped in (not yet tested code)
removed the descriptor from the plugin itself, lets see if we can remove
the acquire and release functions later too.
Declare the plugin interface itself in its first experimental state
