Internal model for managing a set of bookmarks.
the contents of a bookmark changed, like the title or URL.
add the bookmarks in the remote URL to the list.
get the bookmarks as a list. This is a mutable copy of the internal list.
get a TreeModel of the internal model, so GUIs can show the state.
merge the given list into the list.
merge in the bookmarks. Items with the same title are repeated, and folders with the same name are merged. When merging in a remote folder, the entire folder is replaced.
set the bookmarks list. This is used as the internal list, without making a copy.