In addition to the DND feedback, this patch:
- introduces a new var 'BookmarksInsertion' that 'encapsulates' DND feedback
display.
- rewrite the rtl handling related to DND. BookmarksInsertion deals with this
subtleties and the "public" feedback orientation ("before"|"on"|"after")
returned by BookmarksInsertion.getOrientation refers now to the DOM.
- paste and copy commands on the menus now insert after the rclicked element.
The hack that appended everything at the end of the container has been removed
or more accurately replaced by another one that is at least invisible to the
user and we already used for DND. The problem is due a problem with the content
building of containers with siblings (open in tabs stuff) not generated by the
bookmarks template.
- usual small glitch fixing.
