[feature] add the ability to toggle "to-read" and private while viewing an archive.

[masukomi]

I find it annoying to be able to quickly and easily toggle "to-read" and from the list view, but not from the show / archive view. There's a good chance that anyone who's used it for a while is reading it if they're looking at the archives page, and thus would no longer need the post to be marked as "to-read"

Toggling privacy happens much more infrequently, and thus would be a waste of valuable space in the list view (see related Issue #63 - mobile view). But there's not good reason to not add it to the archive view if we're adding a "to-read" toggle.

I'm imagining these would be implemented similarly to the to-read toggle in the list view and live in the right sidebar.