Clean up and Change all gadget's CSS rules to be prefixed by  `div[data-gadget-url$="gadget_document_scanner.html"]`

The http response should return a 200 response in case of success. The response body may contain a local reference of the uploaded image

Request body should contain the image data and the active process relative url (depending on which erp5 context the script is called)

make jslint happy

* change the `extra renderjs` parameters list to pass a Python script to call when a new image is cropped.
* change the gadget to use jio.util.ajax with the script full url (provided by the server)

Change the gadget checkValidity method to return false when:
- no thumbnail has been generated
- a thumbnail upload is in failed state

The default value is a JSON containing 2 keys:
- the relative_url of an active process
- the list of active process image content to aggregate
By default, when the field is rendered for the first time, this tales expression is evaluated and a new active process is created at that point.
So, default json is like: {active_process: 'portal_activities/1234', image_list: []}
* store the active_process relative_url in the gadget state in the render method
* store the image_list in the gadget state in the render_method
* change getContent method to send a json build from the active_process and image_list state

If device_id is propagated to onStateChange, it means we have a new value. Then, check if we have this property is enough to switch

XXX
Allow to show previously uploaded image.
Allow to delete or retry uploading.

Form submittion only send the active process informations.

Stop relying of CSS hide/show attributes.
Instead, only put needed elements in the DOM.

Keep compatibility with existing officejs tests, by keeping the
data-i18n attributes, even if useless.

Chrome will deprecate appcache in the coming weeks.
As appcache has been dropped on Firefox, this change will improve the speed on Firefox.

The service worker only provide a cache for all ERP5JS gadgets.
ERP5JS will still be usable on browser without service worker API.

The list of files to cache is directly added inside the service worker
code, in order to be able to skip the usage of the fetch method (which
does not yet cover all browser HTTP usage).

This list is configurable on the web site level.
No need to change the service worker code directly.

The service worker will be updated as soon as the web site modification date changes.

End user does not need to reload its browser tab.
Only browsing ERP5JS will trigger the service worker update.

When a new update is found, ERP5JS will automatically reload itself if
there is no risk of losing user data input.

An empty appcache is kept, to allow migration of existing client to the
worker automatically.

See 2e3f7a8a

Use the precache script to get the list of gadgets.
Ensure to also check the launcher gadget.

Report subgadget service error.

Replace it by domsugar.

This speed up gadget class generation (handlebars template parsing is
slow).

This attribute is only needed for the translateHTML method.
There is no reason for it to be kept in the final DOM HTML.

Add service worker precache script.

Add service worker precache script

renderJS now correctly handles relative URL.