For the HashAlignment rule, we're using the default `key` style (keys
are aligned and values aren't) instead of the `table` style (both keys
and values are aligned) because, even if we used both in the
application, we used the `key` style a lot more. Furthermore, the
`table` style looks strange in places where there are both very long and
very short keys and sometimes we weren't even consistent with the
`table` style, aligning some keys without aligning other keys.
Ideally we could align hashes to "either key or table", so developers
can decide whether keeping the symmetry of the code is worth it in a
case-per-case basis, but Rubocop doesn't allow this option.
We were using helper methods inside the model; we might as well include
them in the model and use them from anywhere else.
Note we're using a different logic for images and documents methods.
That's because for images the logic was defined in the helper methods,
but for documents the logic is defined in the Documentable concern. In
the past, different documentable classes allowed different content
types, while imageable classes have always allowed the same content
types.
I'm not sure which method is better; for now, I'm leaving it the way it
was (except for the fact that we're removing the helper methods).
