Add a BookmarkThisCapability that can be used to make individual meta items bookmarkable from the browsers instead of implicitly assuming that everythig can be bookmarked.
Use this capability to make albums and artists from Jamendo and Magnatune bookmarkable.

The capability also decides whether advanced or simple filtering ("artist:'foo' AND album:'bar'" vs. "foo" ) is used for creating bookmarks, depending on the capabilities of the collection.

Scriptable servces are now bookmarkable only if they have a search bar, and they always use the simple filtering.

This also takes most of the guesswork of of the NavigationUrlGenerator as it no longer has to guess the source of each meta item.