api: add Repo.set_progress_bar() to the API.

Related: RhBug:1071323
api: expose RepoDict.get_matching() and RepoDict.all() (RhBug:1071323)

Renames get_multiple() to get_matching() and changes the KeyError handling to
be more similar to what the builtin dict.get().

Drops property on all(), dict.values() isn't a property either.