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

- Upload images asynchronously to improve the usability

Add a tales expression as default field value. 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

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

- POST image cropped to backend
  * 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)

- Translate and Update i18n info
- Ajax must return a active process image content UUID
- Add spinner in button to show that we are saving it in background
- Add reference to Active Process. With this, we can search easily active processes used by document scanner and remove them
- Add an alarm which will delete outdated (>5 days old) active_process created by the dialog.
- Improve code to switch cameras in mobiles with more than 2 cameras
- Display intermediate image after get orientation and instantiate Cropper