Reuse Queue created from callback directly.

Mutex execution should be cancellable.
callback should always be cancellable without preventing the mutex to be released.

Seems the .then method never realse the memory if the original promise is kept.
Manually create new promise instead each time.

The inital loaded HTML does not contain anything of renderjs and gets added only after pageload.
Instead of registering init() for the DOMContentLoaded event directly, a deferred promise is used which gets resolve either by the event, or by a manual call of rJS.manualBootstrap().

Tests:
* injects rsvp/renderjs in a blank iframe
* makes sure renderjs is only present after it was injected
* calls manual bootstrap to initialzed renderjs
* creates small test gadget to ensure renderjs is working within the iframe (after bootstrap was executed)

This can be used to catched loading errors from HTML gadget declaration.
This will prevent the parent gadget to fail.

This should improve renderJS usage on slow network.

Use document fragment to add all dependencies with one DOM call only.

Resetting the internal gadget state leads to unexpecting errors, and so,
it was a bad idea.

In case of onStateChange cancellation/error, reset the internal gadget state.
It will simplify the code of each onStateChange function, as developpers will
not have to handle such issue.

Changes on this state should be done by calling the changeState method.

If modifications are detected, an onStateChange callback will be triggered,
with the modified state keys as parameter.

Gadget can now access their DOM element without using not needed asynchronous code.

Jobs are executed on demand only when the gadget is in the DOM.

Calling the same job a second time cancel the previous execution.

This will declare a service to listen to a DOM event on the gadget element.

Browser cancels all ajax requests after the beforepageunload event.
This leads to the global renderJS error handling, which is unpleasant from user point of view.

Altering base url in the iframe gadget resulted in loading resources not from
the gadget iframe url but from the root gadget url. This is a critical issue
when the iframe gadget comes from a different domain

It removes communication timeout with parent iFrame and solve the issue of timeout in case of a high load due to heavy JS processing
/reviewed-on nexedi/renderjs!2

Gadget can now be declared in HTML without any explicit scope.

It is necessary to use dropGadget to completely remove a gadget.

This sandbox download the gadget HTML code and convert it as a dataurl which is loaded in an iframe.
This may help to bypass web browser mixed content policy or CSP restrictions (like inline js).

When a gadget is in iframe, it checks its communication's channel by using timeout 100ms (the only way...).
If a timeout occurs, renderjs considers this gadget has no parent gadget and so, consider it as parent gadget by stopping acquisition.

A service is function which is executed outside the promise tree when the
gadget is attached to the DOM.
Services are stopped when the gadget is removed from the DOM.

You can declare a service with the "declareService" method, which takes a
function as parameter.

Service errors are reported to the parent gadget by acquisition on
"reportServiceError".
If no gadget catched the service error, the application will crash (document
body will display the raw error).