Make it possible to define a layout with one checkbox per widget for bulk edit screen

The bulk edit screen needs checkboxes to be able to tell what fields really need to be changed. Adding a checkbox for each of the widgets makes its clear for the user, so the layout should make it possible to check automatically the checkbox when the corresponding widget is clicked or changed. The map of checked properties should be available in the updated document or object mapped by the layout.

Layout and widget properties are retrieved from the xml contribution, but in some situations it is suseful to be able to set properties from the xhtml file doing the rendering.
For instance, this is useful to set javascript properties (onchange, onclick...) on all widgets of a layout, and can be used to propagate the checkbox id to the widgets.

Some widgets also need this properties to be handled (onchange, onclick, onselect) so they have to be added to Nuxeo JSF components that do not have it. The widgets using templates should be able to get this value too. As these properties may be EL expressions, the layout and widget properties should be exposed to the EL Context so that they are resolved (because using #

, we get an expression that would need to be resolved again)