Feature/taggable keywords

make keywords taggable. added autocomplete and set them as taggable objects 
We should make all the specs more readable. For example, it's not obvious what "Cool Stuff" is. It could be that it's the blog post title or body, but it's not obvious from this test.

Something like this would probably be more readable:

```
create_a_new_blog_post_with_title("Cool stuff")
...
```