improve code to serialize and unserialize errors(AcquisitionError and CancelationError) through jschannel

Also, add IframeSerializationError to handle unhandled type errors

See nexedi/rsvp.js@fa862176

Improve the verbosity of error when using iframe.

Ensure to cancel the ongoing promise if queue is cancelled.

This reduces the number of DOM modifications (only one replace).

This also ensure that the element content is empty.

Previous event listener will also be discarded (and so, reduce memory usage).

declareGadget element parameter can now also be a tag name.

This will simplify error catching.

Contains speed optimizations, mostly by reducing the number of promise created.
This reduce the garbage collection load.

No need to execute async code if the gadget class is already loaded.