Bulk actions for bookmarks.

In this initial version, the new buttons are on the Bookmarks Options popup menu.  I'm not sure if it makes more sense for it to be there on in the #toolbox.  I'm not sure how well the larger menu will work on Android.


Also, I'm not sure what to do about syncing.  Right now the runHooks() just reuses the 'import' message, since it's the only other thing closer to a bulk feature.  But, maybe it makes sense to collect all of the changed data, and send it to the hooks with a 'bulk' message, and let the sync do something more diff based.  I'm not sure what the features of the sync protocol are.