Bug 1109772 - Part 1: move createMockFavicon to Favicons.
Bug 1109772 - Part 2: rename existing Bookmarks class to BookmarksREST.
Bug 1109772 - Part 3: create 'DataAccess' grouping and Bookmarks.swift.
Bug 1109772 - Part 4: lift out ShareItem to be a top-level struct type.
Bug 1108772 - Part 5: eliminate ShareItem.icon.
Bug 1109772 - Part 6: expose Bytes.swift to the rest of the project.
Bug 1109772 - Part 7: add bookmark_folder_closed image.
Bug 1109772 - Pre-refactor refactoring for data access APIs. r=st3fan