Bug 1109772 - Part 8: lift out Account interface.
Bug 1109772 - Part 9: abstract bookmarks and sharing.
Bug 1109772 - Part 9b: update TestBookmarks.
Bug 1109772 - Part 10: transparently include in-memory saved items in Mobile Bookmarks.

Note that this is currently difficult to manually test, because the
client application is distinct from the sharing application!
Review comment: use constants for bookmark root GUIDs.
Review comment: remove errant semicolons.
Review comment: rename createMockFavicon -> createSizedFavicon.
Review comment: have MemoryBookmarkFolder implement SequenceType.
Review comment: make MemoryBookmarkFolder subscriptable.
Merge pull request #37 from mozilla/rnewman/api-refactor

Bug 1109772 - Refactor bookmarks data access API. r=st3fan