Do not run phantomJS test by default.

As renderJS is not compatible with phantomJS (which does not support CSS
loading events), no need to slow down default execution.
Gadgets are now event targets.

The method .on, .off, .trigger have been added.
See RSVP.EventTarget.mixin for full details.

Propagate the events in case of EmbeddedGadget to the parent IframeGadget.