eo: enable priority with event forwarder.

eo: enable priority with event forwarder.

Note: Their isn't any ability to do something like a static array of
events at the moment. It might lead to large memory being used when it
wouldn't be necessary. If that was the case, we could fix it, but it
would require a lot of dynamic hash operation I think.

Reviewed-by: Marcel Hollerbach <marcel-hollerbach@t-online.de>
Differential Revision: https://phab.enlightenment.org/D7482