Improve the object and class editors

Object editor:

• better access to objects (ability to see more than one object at a time)
• links to edit only one object (and to return to all objects)
• faster object delete with AJAX

Class editor:

• ability to see more than one property at a time
• clearer display of the property type
• new icons for each property type
• property reordering with Drag&Drop
• hide in the UI unused metaproperties (tooltip, customDisplay, unmodifiable, contenttype)
• list existing classes when the current document does not define a class