Scopes on associations

Punch a hole in the association_proxy for scopes. Also inject the parents id if needed.

Addresses https://github.com/remiprev/her/issues/215
does it mean we need to specify `collection_path` on the association's model if we want to call the scopes on it? is there any way to get around it?

This is the official document example,

```ruby
@user.comments.where(approved: 1)
# GET "/users/1/comments?approved=1"
# => [#<Comment id=1>]
```

wonder if we could just call it without adding that `collection_path`:

```ruby
# want this
@user.comments.approved
# GET "/users/1/comments?approved=1"

# current(without specifying collection_path on Comment model)
# GET "/comments?approved=1"
```