- the child gadget calls a blocking acquiredMethod on the parent.
- the child gadget cancel the acquiredMethod call
- the child gadget calls another acquiredMethod on the parent to verify that the cancellation has been correctly propagated to the parent.

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.

Reuse Queue created from callback directly.