add: PadletBookmarkSpec (was missing).
WIP: PadletBookmark and Controller: Allow more than one pad let per user

[#44996983]
https://www.pivotaltracker.com/story/show/44996983
BookmarksController (&etc.) : Make bookmarks sortable.
Bookmarks.js.coffee: client-side editing of bookmarks. Styles, & view.

[#44996983]
https://www.pivotaltracker.com/story/show/44996983
BookmarksController: (minor) remove comments.