Include folders in bookmark titles.

Addresses #675.

Approach:
  - Bookmark titles are augmented with the titles of their folders (right up the hierarchy).

Examples:
1. A bookmark titled `BBC Radio 4` becomes `/Other Bookmarks/Media/BBC/Radio/BBC Radio 4`.
2. Mobile bookmarks show up under `/Mobile Bookmarks/...`

Pros:
  - Searching bookmark folders from the vomnibar works well.
  - A search like `/bb` is probably enough to pick out just the bookmarks under the `BBC` folder.
  - A search like `/mo` is probably enough to pick out only mobile bookmarks.
  - A search like `soc` will match bookmarks in/under a folder `.../Social/...`.

Cons:
  - If folder names are very long, or if folders are highly nested, the title wraps in the vomnibar and doesn't look great.  (The same problem arises already for bookmarks with very long titles.)
  - So there's a new option included with this PR, it defaults to `false` (off).  And the proliferation of options is something which is generally best avoided.