Adding question methods to all the associations

This PR adds question methods to all the associations. The question mark methods allow us to know if there are records in a association. Example...

This makes it possible to use...

```
post = Post.create(title: "MyFirstPost")
post.comments?                                              # => false

post = Post.create(title: "MyFirstPost")
post.comments.create!
post.comments?                                              # => true
```

Instead of...

```
post = Post.create(title: "MyFirstPost")
post.comments.size > 0                                   # => false
```