New *RecentChanged similar to *RecentAdded

[Dustcap]

@simoncn:
In post #2 you stated not wanting an indexed solution and prefered a "special tag" based solution similar to #AudioQuality.
For me that would be fine and since #AudioQuality has categories, I suggested some for #RecentlyModified.

Since then we're talking about an indexed solution, as far as I understand the posts.

If you'd prefer an indexed solution after all, I would tend to the yearMonth option of the tagOptions property to have the index entries grouped as yyyy-mm.